Hi Wesley!
The expired link error sounds like there may be an issue with how your network’s domain has been configured. What does network structure look like? Is the https://www.motoplus.nl your canonical domain, or without the www? Which one is defined in your wp-config.php?
As for the invalid user ID: have you ensured these users that you are attempting to give exist in the entire network? In other words, is there a chance you are attempting to give super admin rights to a user that only exists on a subsite?
Do you happen to have any additional information about these errors, such as error logs?
