To keep a high quality among all WhatsApp accounts on the DSGVO compliant WhatsApp Business API, META has some (commercial) guidelines that users and their accounts have to comply with.
Sometimes this results in incorrect restrictions, against which a re-verification has to be submitted from the customer side to get the blocked WhatsApp account live again.
You can request this review via your account quality at: https://business.facebook.com/accountquality.
Make sure that you are in the correct META business account in the account quality (check top left-hand corner)!
Here you can also see the status of your WhatsApp Business API accounts under the "Meta business accounts" tab at the very bottom and, by clicking on it, view the status and request a review if necessary.