Four WhatsApp rules that explain almost every rejection we see.
The 24-hour window and the template. It is failure number one —one customer collected 68 rejections from it— and it is step ④: inside the window you send free-form text, outside it only an approved template. If the concept isn't clear yet, read that one first; this is just the operational rule. It unlocks: writing when the customer didn't write first.
Files go by a DIRECT link to the file. A Drive or Dropbox link returns a page, not the file, and Meta can't download it: 26 failures across two customers from this alone. It has to be a public URL that answers with the file. It unlocks: sending invoices, receipts and photos.
Your contact list has to be clean. A number that isn't on WhatsApp bounces, and bouncing repeatedly lowers your number's quality rating — and with a lower rating Meta lowers your ceiling. One customer collected 32 rejections this way. It unlocks: not losing reach to a stale list.
When the same error repeats (5 times in an hour), the panel tells you on the Activity screen with what to do about it, not just with a count.
All of these rejections arrive with a stable code in lastErrorCode — the full catalog is in the Complete level of this documentation.