Yea, just set that field to ClientAndServer. ATT_MAX is an invalid option that is due to the last update which needed to rename those fields for MacOS compilation.
But, in regard to your question, you can override the Location field on the Spawn Actor task (hit the + button next to the transform) and you can simply get your SelfActor -> Cast it to your Character -> Get your Weapon -> Get the Socket Transform from your weapon and return that.
There is a Discord server someone setup (it’s in this thread), I know both myself and AngelV frequent the UnrealSlackers Discord from time to time.