WMS service fails to display in ArcGIS Online applications

Description

When the WMS service is added using the EPSG:900913 coordinate system instead of the expected EPSG:3857 (Web Mercator), although both codes refer to very similar projections, the difference in their identifiers can lead to rendering issues in ArcGIS Online applications.
As a result, the WMS layer does not display, even though it has been successfully added to the map, as shown in the image below.

Cause

When adding a WMS service, ArcGIS Online automatically selects one of the available coordinate reference systems (CRS) declared by the WMS server. If the server offers EPSG:900913 (an older, unofficial identifier for Web Mercator), ArcGIS Online may choose it instead of the recommended EPSG:3857.

Solution or Workaround

To ensure the WMS service displays correctly in ArcGIS Online applications, it should be added as a layer with the Add Custom Parameter option.

• for Parameter, use CRS
• for Value set it to EPSG:3857