When sending campaigns, they only appear as 'accepted' but the recipient does not receive them?
Make sure you have added a payment method to the customer’s Meta Business account.
Why does the customer have to pay for each conversation on Meta Business account than through us?
You need to be a “Solution Partner” in order for you to be able to manage billing on behalf of your customers. One of the prerequisites of being a solution Partner is to have Embedded Signup. Check here https://business.whatsapp.com/partners/become-a-partner