New to buying with Crypto

Here is scenario:
I want to buy a software service online with crypto. I register on the website selling the service. I put the service in my shopping cart and choose to pay with crypto. I am then sent to page with QR code to scan. I scan with phone to pay with coinbase, or i enter his wallet address into app on my phone. How does the seller then know to credit that transaction to the account I registered on his website? Since my crypto wallet is on my phone but I am purchasing a service from a website on pc? I don't understand how he knows that transaction on my phone was related to an item i put in a shopping cart on my pc?

Is the address I sent it to a one-time unique purchase address so then he knows this payment is related to the QR code I scanned with my phone from my computer screen?

I hope I explained it well. Sorry I am new to making purchases with bitcoin. I have bought and sold crypto before, but never used it to make a purchase of an item.

@[Only registered and activated users can see links. Click Here To Register...]

Your phone reads the QR code which includes information about the address and amount to be send and decodes it for the wallet. For bitcoin it looks like:

[Only registered and activated users can see links. Click Here To Register...]

as soon as you make an order, an address gets created ONLY for you. the seller associates this address with your outstanding payment. as soon as the coins arrive, he knows you paid. doesnt matter if you pay via phone or browser or whatever.

thats basicly how all cryptopayments work

The details shown to you are unique to you, as soon as you send the specific crypto amount to the specific address that page where you scanned the QR code should automatically update to say that the payment has been added to the blockchain. Just keep in mind its not instant and will need "confirmations" BTC for example usually requires 2 "confirmations" but don't worry once its sent it will go through it can just take some time. BTC can take a little long sometimes. I recommend paying in LTC since the fees are pretty low and its reasonably fast