Go to the BP_CharacterComponent and create a new custom event called MulticastAttachWeapon and set it to Multicast and tick Reliable.

Then add a new input called Target and set its type to Scene Component.

Then add a new input called Parent and set its type to Scene Component.

Then add a new input called Socket and set its type to Name.

Then copy the image below, location at top of screenshot.

Then copy the images below, locations at top of screenshots.