@hube2 yes correct and it works for creating a user. But when I try to make a change to a user this function runs and causes an error because the user id already exists. So I suspect it is outputting something other than just user Id which is causing the above string error.
Basically updating the custom post type users results in the error due to line
update_field('field_602ce62b11720', $incident, 'user_'.$user_id)
