Make sure that the ID field in the view is a "key attribute" (check the semantics layer).
If that is the case, then change your service to this:
service namespace "sap.solman"{
"sap.solman::EXTEND_ATTR_VIEW" as "mount" keys ("ID") ;
}
Here's the changes:
You don't need the full path on the key field, just the field name.
Also, you don't need to include the .attributeview file name extension on your view name.
I don't think the forward slash will work, in my local project I have the double colon ::, but I am not sure of your complete setup. Try the service definition above and I hope it works for you.
