Found that the REMOVEINVITE variable in myplex.py had a URL of "'https://plex.tv/api/invites/requested/{userId}?friend=1&server=1&home=1'"
Because REMOVEINVITE is the alternative when evaluating user.friend to False on line 384 of myplex.py, the URL should read: "'https://plex.tv/api/invites/requested/{userId}?friend=1&server=1&home=0'"
Verified this by manually removing a user that hadn't accepted an invite, while watching the call that was made in DevTools.
An example of those request headers is attached.
RemoveUserThatHasntAcceptedInvite-REQUEST HEADERS EXAMPLE.txt