The JavaScript API esri/layers/WMSLayer class does not support URLs containing parameter names written in mixed case.

解决办法

Leave out the parameters when setting the URL of the WMSLayer. For instance, instead of setting the URL to https://sampleserver6.arcgisonline.com/arcgis/services/USA/MapServer/WMSServer?Service=WMS&version=1.3.0&request=GetCapabilities, set it to https://sampleserver6.arcgisonline.com/arcgis/services/USA/MapServer/WMSServer. The API automatically applies the correct parameters when sending the GetCapabilities request.

重现步骤