Pool unexpected argument when trying to patch pool member

Unless you have a very specific need for a custom role, I would suggest you to use a ready-made role. Find the one most appropriate from Manual Chapter: User Roles. If you really want to use a custom role, take a look at iControl REST Fine-Grained Role Based Access Control. Because it's tricky, you may want to contact F5 Professional Services for consultation.

For your information, here's a curl command for creating a new user with the role "operator".

curl https:///mgmt/tm/auth/user -X POST -H "Content-type: application/json" \
  -d '{"name":"newUser", "password":"newPassword", \
       "shell":"tmsh", "partitionAccess":[{"name":"all-partitions", "role":"operator"}]}'