Hey, ​@praneethm!

Check if you're replying to these contacts withing the 24h message window. 

And if you're trying to make a “first contact” with your contacts, you must use Message Templates to initiate a conversation.

https://help.manychat.com/hc/en-us/articles/14281326740124-How-to-use-WhatsApp-Messages-Templates-in-Manychat

I’ts a user initiated conversation and it is  in the 24 hours window, but still message is not going to the customer, in manychat it shows as sent

That's super odd… It could also be some restriction from Meta's side. Take a look at your WhatsApp Manager in Meta Business Suite. Sometimes you find more info around there.

I'd also suggest opening a ticket to Manychat's Support Team: How to get support from Manychat – Manychat Help

They will be able to investigate it further.