Just tested it, the page successfully called back. Great start!

Invoice hDVBNEg4FEKLH4oyQM payed!
You still need to compare the transfered amount to the required amount on your website!
This is only the callback URL providing all those details (see below)

{"status":"success","memo":"hDVBNEg4FEKLH4oyQM","from":"trending","to":"steempayments","amount":"0.001 SBD"}