BTCPay server from Umbrel works ONLY behind TOR.
So you have 2 options:
- use your webshop with payment on onion page (from your Umbrel BTCPay server)
- adapt your Umbrel machine to use clearnet for BTCpay. Here is a guide for LNbits that can be adapted for BTCpay module.
But remember: do this only IF YOU KNOW WHAT ARE YOU DOING.