diff --git a/CryptoExchange.Net.UnitTests/CallResultTests.cs b/CryptoExchange.Net.UnitTests/CallResultTests.cs
index dd52d41..ab75100 100644
--- a/CryptoExchange.Net.UnitTests/CallResultTests.cs
+++ b/CryptoExchange.Net.UnitTests/CallResultTests.cs
@@ -112,7 +112,7 @@ namespace CryptoExchange.Net.UnitTests
         {
             var result = new WebCallResult<TestObjectResult>(
                 System.Net.HttpStatusCode.OK,
-                new List<KeyValuePair<string, IEnumerable<string>>>(),
+                new KeyValuePair<string, string[]>[0],
                 TimeSpan.FromSeconds(1),
                 null,
                 "{}",
@@ -120,7 +120,7 @@ namespace CryptoExchange.Net.UnitTests
                 "https://test.com/api",
                 null,
                 HttpMethod.Get,
-                new List<KeyValuePair<string, IEnumerable<string>>>(),
+                new KeyValuePair<string, string[]>[0],
                 ResultDataSource.Server,
                 new TestObjectResult(),
                 null);
@@ -142,7 +142,7 @@ namespace CryptoExchange.Net.UnitTests
         {
             var result = new WebCallResult<TestObjectResult>(
                 System.Net.HttpStatusCode.OK,
-                new List<KeyValuePair<string, IEnumerable<string>>>(),
+                new KeyValuePair<string, string[]>[0],
                 TimeSpan.FromSeconds(1),
                 null,
                 "{}",
@@ -150,7 +150,7 @@ namespace CryptoExchange.Net.UnitTests
                 "https://test.com/api",
                 null,
                 HttpMethod.Get,
-                new List<KeyValuePair<string, IEnumerable<string>>>(),
+                new KeyValuePair<string, string[]>[0],
                 ResultDataSource.Server,
                 new TestObjectResult(),
                 null);
diff --git a/CryptoExchange.Net.UnitTests/TestImplementations/TestRestClient.cs b/CryptoExchange.Net.UnitTests/TestImplementations/TestRestClient.cs
index 8d1ef36..f1841d3 100644
--- a/CryptoExchange.Net.UnitTests/TestImplementations/TestRestClient.cs
+++ b/CryptoExchange.Net.UnitTests/TestImplementations/TestRestClient.cs
@@ -17,6 +17,7 @@ using Microsoft.Extensions.Logging;
 using CryptoExchange.Net.Clients;
 using CryptoExchange.Net.SharedApis;
 using Microsoft.Extensions.Options;
+using System.Linq;
 
 namespace CryptoExchange.Net.UnitTests.TestImplementations
 {
@@ -49,13 +50,13 @@ namespace CryptoExchange.Net.UnitTests.TestImplementations
             response.Setup(c => c.IsSuccessStatusCode).Returns(true);
             response.Setup(c => c.GetResponseStreamAsync()).Returns(Task.FromResult((Stream)responseStream));
             
-            var headers = new Dictionary<string, IEnumerable<string>>();
+            var headers = new Dictionary<string, string[]>();
             var request = new Mock<IRequest>();
             request.Setup(c => c.Uri).Returns(new Uri("http://www.test.com"));
             request.Setup(c => c.GetResponseAsync(It.IsAny<CancellationToken>())).Returns(Task.FromResult(response.Object));
             request.Setup(c => c.SetContent(It.IsAny<string>(), It.IsAny<string>())).Callback(new Action<string, string>((content, type) => { request.Setup(r => r.Content).Returns(content); }));
-            request.Setup(c => c.AddHeader(It.IsAny<string>(), It.IsAny<string>())).Callback<string, string>((key, val) => headers.Add(key, new List<string> { val }));
-            request.Setup(c => c.GetHeaders()).Returns(() => headers);
+            request.Setup(c => c.AddHeader(It.IsAny<string>(), It.IsAny<string>())).Callback<string, string>((key, val) => headers.Add(key, new string[] { val }));
+            request.Setup(c => c.GetHeaders()).Returns(() => headers.ToArray());
 
             var factory = Mock.Get(Api1.RequestFactory);
             factory.Setup(c => c.Create(It.IsAny<HttpMethod>(), It.IsAny<Uri>(), It.IsAny<int>()))
@@ -84,7 +85,7 @@ namespace CryptoExchange.Net.UnitTests.TestImplementations
            
             var request = new Mock<IRequest>();
             request.Setup(c => c.Uri).Returns(new Uri("http://www.test.com"));
-            request.Setup(c => c.GetHeaders()).Returns(new Dictionary<string, IEnumerable<string>>());
+            request.Setup(c => c.GetHeaders()).Returns(new KeyValuePair<string, string[]>[0]);
             request.Setup(c => c.GetResponseAsync(It.IsAny<CancellationToken>())).Throws(we);
 
             var factory = Mock.Get(Api1.RequestFactory);
@@ -108,12 +109,12 @@ namespace CryptoExchange.Net.UnitTests.TestImplementations
             response.Setup(c => c.IsSuccessStatusCode).Returns(false);
             response.Setup(c => c.GetResponseStreamAsync()).Returns(Task.FromResult((Stream)responseStream));
 
-            var headers = new Dictionary<string, IEnumerable<string>>();
+            var headers = new List<KeyValuePair<string, string[]>>();
             var request = new Mock<IRequest>();
             request.Setup(c => c.Uri).Returns(new Uri("http://www.test.com"));
             request.Setup(c => c.GetResponseAsync(It.IsAny<CancellationToken>())).Returns(Task.FromResult(response.Object));
-            request.Setup(c => c.AddHeader(It.IsAny<string>(), It.IsAny<string>())).Callback<string, string>((key, val) => headers.Add(key, new List<string> { val }));
-            request.Setup(c => c.GetHeaders()).Returns(headers);
+            request.Setup(c => c.AddHeader(It.IsAny<string>(), It.IsAny<string>())).Callback<string, string>((key, val) => headers.Add(new KeyValuePair<string, string[]>(key, new string[] { val })));
+            request.Setup(c => c.GetHeaders()).Returns(headers.ToArray());
 
             var factory = Mock.Get(Api1.RequestFactory);
             factory.Setup(c => c.Create(It.IsAny<HttpMethod>(), It.IsAny<Uri>(), It.IsAny<int>()))
@@ -186,7 +187,7 @@ namespace CryptoExchange.Net.UnitTests.TestImplementations
             return await SendRequestAsync<T>(new Uri("http://www.test.com"), HttpMethod.Get, ct, requestWeight: 0);
         }
 
-        protected override Error ParseErrorResponse(int httpStatusCode, IEnumerable<KeyValuePair<string, IEnumerable<string>>> responseHeaders, IMessageAccessor accessor)
+        protected override Error ParseErrorResponse(int httpStatusCode, KeyValuePair<string, string[]>[] responseHeaders, IMessageAccessor accessor)
         {
             var errorData = accessor.Deserialize<TestError>();
 
diff --git a/CryptoExchange.Net/Clients/RestApiClient.cs b/CryptoExchange.Net/Clients/RestApiClient.cs
index 0ee0af1..3c22555 100644
--- a/CryptoExchange.Net/Clients/RestApiClient.cs
+++ b/CryptoExchange.Net/Clients/RestApiClient.cs
@@ -638,7 +638,7 @@ namespace CryptoExchange.Net.Clients
                 paramString = $" with request body '{request.Content}'";
 
             var headers = request.GetHeaders();
-            if (headers.Count != 0)
+            if (headers.Length != 0)
                 paramString += " with headers " + string.Join(", ", headers.Select(h => h.Key + $"=[{string.Join(",", h.Value)}]"));
 
             TotalRequestsMade++;
@@ -768,7 +768,7 @@ namespace CryptoExchange.Net.Clients
         /// <param name="accessor">Data accessor</param>
         /// <param name="responseHeaders">The response headers</param>
         /// <returns>Null if not an error, Error otherwise</returns>
-        protected virtual Error? TryParseError(IEnumerable<KeyValuePair<string, IEnumerable<string>>> responseHeaders, IMessageAccessor accessor) => null;
+        protected virtual Error? TryParseError(KeyValuePair<string, string[]>[] responseHeaders, IMessageAccessor accessor) => null;
 
         /// <summary>
         /// Can be used to indicate that a request should be retried. Defaults to false. Make sure to retry a max number of times (based on the the tries parameter) or the request will retry forever.
@@ -943,7 +943,7 @@ namespace CryptoExchange.Net.Clients
         /// <param name="responseHeaders">The response headers</param>
         /// <param name="accessor">Data accessor</param>
         /// <returns></returns>
-        protected virtual Error ParseErrorResponse(int httpStatusCode, IEnumerable<KeyValuePair<string, IEnumerable<string>>> responseHeaders, IMessageAccessor accessor)
+        protected virtual Error ParseErrorResponse(int httpStatusCode, KeyValuePair<string, string[]>[] responseHeaders, IMessageAccessor accessor)
         {
             var message = accessor.OriginalDataAvailable ? accessor.GetOriginalString() : "[Error response content only available when OutputOriginal = true in client options]";
             return new ServerError(message);
@@ -956,7 +956,7 @@ namespace CryptoExchange.Net.Clients
         /// <param name="responseHeaders">The response headers</param>
         /// <param name="accessor">Data accessor</param>
         /// <returns></returns>
-        protected virtual ServerRateLimitError ParseRateLimitResponse(int httpStatusCode, IEnumerable<KeyValuePair<string, IEnumerable<string>>> responseHeaders, IMessageAccessor accessor)
+        protected virtual ServerRateLimitError ParseRateLimitResponse(int httpStatusCode, KeyValuePair<string, string[]>[] responseHeaders, IMessageAccessor accessor)
         {
             var message = accessor.OriginalDataAvailable ? accessor.GetOriginalString() : "[Error response content only available when OutputOriginal = true in client options]";
 
diff --git a/CryptoExchange.Net/Interfaces/IRequest.cs b/CryptoExchange.Net/Interfaces/IRequest.cs
index 7f7414a..72ebe59 100644
--- a/CryptoExchange.Net/Interfaces/IRequest.cs
+++ b/CryptoExchange.Net/Interfaces/IRequest.cs
@@ -54,7 +54,7 @@ namespace CryptoExchange.Net.Interfaces
         /// Get all headers
         /// </summary>
         /// <returns></returns>
-        Dictionary<string, string[]> GetHeaders();
+        KeyValuePair<string, string[]>[] GetHeaders();
 
         /// <summary>
         /// Get the response
diff --git a/CryptoExchange.Net/Requests/Request.cs b/CryptoExchange.Net/Requests/Request.cs
index 47428e6..23f1f1c 100644
--- a/CryptoExchange.Net/Requests/Request.cs
+++ b/CryptoExchange.Net/Requests/Request.cs
@@ -67,9 +67,9 @@ namespace CryptoExchange.Net.Requests
         }
 
         /// <inheritdoc />
-        public Dictionary<string, string[]> GetHeaders()
+        public KeyValuePair<string, string[]>[] GetHeaders()
         {
-            return _request.Headers.ToDictionary(h => h.Key, h => h.Value.ToArray());
+            return _request.Headers.Select(h => new KeyValuePair<string, string[]>(h.Key, h.Value.ToArray())).ToArray();
         }
 
         /// <inheritdoc />
diff --git a/CryptoExchange.Net/SharedApis/Interfaces/Rest/Futures/IFuturesOrderRestClient.cs b/CryptoExchange.Net/SharedApis/Interfaces/Rest/Futures/IFuturesOrderRestClient.cs
index cb84dde..8b78ab9 100644
--- a/CryptoExchange.Net/SharedApis/Interfaces/Rest/Futures/IFuturesOrderRestClient.cs
+++ b/CryptoExchange.Net/SharedApis/Interfaces/Rest/Futures/IFuturesOrderRestClient.cs
@@ -21,11 +21,11 @@ namespace CryptoExchange.Net.SharedApis
         /// <summary>
         /// Supported order types
         /// </summary>
-        IEnumerable<SharedOrderType> FuturesSupportedOrderTypes { get; }
+        SharedOrderType[] FuturesSupportedOrderTypes { get; }
         /// <summary>
         /// Supported time in force
         /// </summary>
-        IEnumerable<SharedTimeInForce> FuturesSupportedTimeInForce { get; }
+        SharedTimeInForce[] FuturesSupportedTimeInForce { get; }
         /// <summary>
         /// Quantity types support
         /// </summary>
diff --git a/CryptoExchange.Net/SharedApis/Models/Options/Endpoints/PlaceFuturesOrderOptions.cs b/CryptoExchange.Net/SharedApis/Models/Options/Endpoints/PlaceFuturesOrderOptions.cs
index d989a78..1a4980f 100644
--- a/CryptoExchange.Net/SharedApis/Models/Options/Endpoints/PlaceFuturesOrderOptions.cs
+++ b/CryptoExchange.Net/SharedApis/Models/Options/Endpoints/PlaceFuturesOrderOptions.cs
@@ -25,8 +25,8 @@ namespace CryptoExchange.Net.SharedApis
             PlaceFuturesOrderRequest request,
             TradingMode? tradingMode,
             TradingMode[] supportedApiTypes,
-            IEnumerable<SharedOrderType> supportedOrderTypes,
-            IEnumerable<SharedTimeInForce> supportedTimeInForce,
+            SharedOrderType[] supportedOrderTypes,
+            SharedTimeInForce[] supportedTimeInForce,
             SharedQuantitySupport quantitySupport)
         {
             if (request.OrderType == SharedOrderType.Other)
diff --git a/CryptoExchange.Net/SharedApis/Models/Options/Subscriptions/SubscribeKlineOptions.cs b/CryptoExchange.Net/SharedApis/Models/Options/Subscriptions/SubscribeKlineOptions.cs
index f46bd74..f6c4d7f 100644
--- a/CryptoExchange.Net/SharedApis/Models/Options/Subscriptions/SubscribeKlineOptions.cs
+++ b/CryptoExchange.Net/SharedApis/Models/Options/Subscriptions/SubscribeKlineOptions.cs
@@ -13,7 +13,7 @@ namespace CryptoExchange.Net.SharedApis
         /// <summary>
         /// Kline intervals supported for updates
         /// </summary>
-        public IEnumerable<SharedKlineInterval> SupportIntervals { get; }
+        public SharedKlineInterval[] SupportIntervals { get; }
 
         /// <summary>
         /// ctor
diff --git a/CryptoExchange.Net/Testing/Implementations/TestRequest.cs b/CryptoExchange.Net/Testing/Implementations/TestRequest.cs
index 32ea87f..dc6ba5a 100644
--- a/CryptoExchange.Net/Testing/Implementations/TestRequest.cs
+++ b/CryptoExchange.Net/Testing/Implementations/TestRequest.cs
@@ -10,7 +10,7 @@ namespace CryptoExchange.Net.Testing.Implementations
 {
     internal class TestRequest : IRequest
     {
-        private readonly Dictionary<string, string[]> _headers = new Dictionary<string, string[]>();
+        private readonly List<KeyValuePair<string, string[]>> _headers = new();
         private readonly TestResponse _response;
 
         public string Accept { set { } }
@@ -32,10 +32,10 @@ namespace CryptoExchange.Net.Testing.Implementations
 
         public void AddHeader(string key, string value)
         {
-            _headers.Add(key, new[] { value });
+            _headers.Add(new KeyValuePair<string, string[]>(key, new[] { value }));
         }
 
-        public Dictionary<string, string[]> GetHeaders() => _headers;
+        public KeyValuePair<string, string[]>[] GetHeaders() => _headers.ToArray();
 
         public Task<IResponse> GetResponseAsync(CancellationToken cancellationToken) => Task.FromResult<IResponse>(_response);