@Michel Jonker Thank you for posting this question in Microsoft Q&A. It is not possible for users to manually restart APIM service/instances as described in other thread.
When a subscription is deactivated, all resources associated with that subscription are also suspended, including APIM. Once your subscription is reactivated, it may take some time for Azure API Management to detect that the backend services are available again.
If you are still experiencing issues with your APIM, I would suggest you open a ticket to our support team to investigate and mitigate this issue as quickly as possible.
Do you have a support plan with us? If not, I can assist you in creating one-time free technical support for you. Let me know your thoughts.