Are you copy-pasting the same message across many chats? If so, try varying them a little.
Infuriating, I know.

The thing is, Meta is changing how they price messages sent on the WhatsApp Business API (they’ll start charging for every single message now) and as such they’ve gone haywire trying to catch and ban unofficial WhatsApp Automation APIs.
If you send the same message across a couple contacts it’s already enough to flag you. And if you’re using WhatsApp Web it’s even worse.

I too wish my country’s communications wasn’t so Intertwined with this garbage.