This!! you can use btcpay server, and create a store account. Then you can generate a pos button url so customers can pay with btc onchain or lightning. For example I created a POS payment button web app, so a merchant can set up an account in a btcpay server (a server of his own or a server from a trusted friend, relative) And install the configured app in his/her pos devices or mobile phones and charge with btcpay with ease (selecting any fiat reference he wants)

If web based solution like BTCPay Server, SatSale is also a lightweight alternative. https://github.com/SatSale/SatSale

The current CoinOS cannot do this, unless one runs their own CoinOS instance on their own domain. (which would, today, take a "bit of set up").

However, CoinOS founder shares his planned solution here:

So the payments received (e.g., using the CoinOS PoS interface) could be protected because of the PIN being required in order to spend, and then those funds would be swept (either immediately or eventually, depending on how that sweep feature is designed) to a non-custodial destination.