Article: https://developer.roblox.com/en-us/api-reference/callback/RemoteFunction/OnServerInvoke
Offending line:
The OnServerInvoke event fires the bound functions in Scripts when RemoteFunction:InvokeServer is called by the server from a LocalScript.
This is wrong because InvokeServer can only be called from the client.
It should say:
… RemoteFunction:InvokeServer is called by the client …
UPDATE 1/25/2021 solved!