Existing users receive the organization invitation email and click on the Accept invitation button taking them to a Sign up form where the email address is pre-filled and the field is grayed out.
They are redirected to
/u/signup/invitation , not
/u/login/invitation in the organization invitation flow, and they must click “Already have an account? Login” to navigate away from the signup prompt.
We suggest the below workaround.
Add users to the organization directly instead of sending them the invitation.