Fixed regression coming from #1290 #1297

src/sdk/CHANGELOG.md

@@ -29,6 +29,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Admin library: Extra parameters to configure the SharePoint Add-In and Azure ACS principal loading [jansenbe - Bert Jansen]
 - Changed `IList.DraftVersionVisibility` to use enum `DraftVisibilityType` instead of an `int` #1286 [jansenbe - Bert Jansen]
 - Fixing URL too long issue when downloading files #1290 [koenzomers - Koen Zomers]
+- Fixed regression coming from #1290 #1297 [jansenbe - Bert Jansen]
 
 ## [1.10.0]
 

src/sdk/PnP.Core/Services/Core/Query/QueryClient.cs

@@ -164,7 +164,16 @@ private static async Task<ApiCallRequest> BuildGetAPICallRestAsync<TModel>(BaseD
                 // In .NET Framework to ToString() of a NameValueCollection will use HttpUtility.UrlEncodeUnicode under
                 // the covers resulting in issues. So we decode and encode again as a workaround. This code produces the 
                 // same result when used under .NET5/Core versus .NET Framework
-                sb.Append($"?{queryString.ToEncodedString()}");
+
+                // The base query string can already contain a URL parameter (e.g. _api/Web/getFileByServerRelativePath(decodedUrl=@u)?@u='<server relative url>')
+                if (baseApiCall.Contains('?'))
+                {
+                    sb.Append($"&{queryString.ToEncodedString()}");
+                }
+                else
+                {
+                    sb.Append($"?{queryString.ToEncodedString()}");
+                }
             }
 
             // Create ApiCall instance and call the override option if needed