When designing Pay With Ether we wanted it to be as simple as possible to both accept ETH on your site, as well as pay with it on someone else’s.
Easiest Solution: Pay the Exact Amount
After selecting PayWithEther at checkout, you’ll be presented with a very precise amount of ether to send to the vendor. Only you send this exact amount will PayWithEther automagically recognise your payment. If you send even a fraction less or more, you’ll have to contact the vendor to get them to resolve it manually.
Foolproof Solution: Use MetaMask or MyEtherWallet/MyCrypto
Both MetaMask and MyEtherWallet/MyCrypto allow you to add data to your transaction, it’s as simple as you’d expect. MetaMask is especially useful since it allows you to interact with all kinds of Ethereum websites. In fact, if you use MetaMask on a website using PayWithEther, you’ll get this shiny lovely button which does all the hard work for you!
If you choose to go with MyEtherWallet, you’ll see a data field when you start to create a transaction, like this:
But do note, you’ll have to click the little “+ Advanced, Add Data” link before the field shows up.
Hopefully that makes things a lot easier, and you can be paying with Ether like a pro in no time!