"Some Plasson fittings, according to their specification, don't have electrodes at one of their outlets. In real-life, a socket welded at that outlet, so in Revit, the user needs to add the socket manually.
As you place those special fittings, a notification appears to remind you about that.
Plasson coupler fitting can be easily added to the system to provide a proper connection.
After adding the coupler, you can hide the warning for specific instance using the 'tick box' under the object ""Properties.""
To hide the warning for all instances in a project, you can turn off the visibility for subcategory ""Warning"" in the ""Pipe Fittings"" category."