Building your app
Webhook
A webhook is a message another service sends to your app the moment something happens, such as a customer paying, so your app can react without having to ask.
Also called web hook
A payment provider, for example, sends one to an address on your backend (the part of your app that runs on a server) after each payment. Your app then unlocks the account. If that address is wrong or down, the payment goes through but your app never hears about it.
When this shows up
Example, not a real founder: a customer pays, gets a receipt, and emails you because their account is still locked. The webhook was pointing at your old test address, so your live app never learned about the payment.
What to do next
Open the webhook log in your payment provider's settings and check that recent events reached your live address and got a success reply.