Could it be that you are running WordPress on a machine in your local network?
Deposit notifications come to your WordPress from the CoinPayments platform via their IPN mechanism. This is HTTP/HTTPS requests coming from CoinPayments. If your installation is not facing the outside world you will either have to install on a VPS or otherwise set up your firewall to forward these requests.
Check your IPN history in CoinPayments and see if the notifications succeed.
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