Hi @LSlooten ,
While you mentioned that the contacts are using the latest version of WhatsApp, double-check to confirm that they have indeed updated to the most recent version. Sometimes, even small updates can impact compatibility.
Also check the limit of the WA messages. A limit of 1000 conversations per month is shared by all your connected WhatsApp business accounts. The day of the month that the limit resets depends on the date you first purchased a Marketing Hub or Service Hub Professional or Enterprise subscription. For example, if your subscription began on October 28, the limit will reset on the 28th of each month.
Check this article for more info.
Hope this helps!
Thanks.