Let's say I have a service that requires that a user send some XLM to another account in order to activate their account, what's the best way to actually verify when it's been paid?
I can think of a few options:
Query the account directly and look for payment operations to it — poll this on a semi-regular basis and keep of the cursor.
Use the EventSource streaming API and look for payment messages that come in. You'd have to be careful that you don't miss a message for whatever reason (service goes down, network partition)
Any others? What do services use for this in practice?