Check this: https://help.manychat.com/hc/en-us/articles/15580879039388-Why-WhatsApp-messages-are-sometimes-not-delivered
Also, make sure you have funds on your Manychat Wallet, and that the numbers are written correctly.
Lastly, check on Settings > Logs to see if you find any errors.
To increase the messages limit, check this: https://help.manychat.com/hc/en-us/articles/14281346817308-WhatsApp-messages-sending-limits
The easy formula I’ve found is this: send 50% or more of your limit for 4-5 consecutive days while keeping the rating green. And most likely by the 5th or 6th day you get upgraded to the next level.
So if you’re at 1000 messages per day, send 500+ per day for 4-5 consecutive days and you get bumped up.
It’s not a scientific formula, but it’s worked so far most of the time!