When a payment is processed via the Square integration in your MassageBook account, MassageBook sends the MassageBook receipt # to Square in what's called the "Note". To find the Square transaction that corresponds with a specific receipt in MassageBook, you just need to search your Square transactions list by "Note" using the MassageBook Receipt number.
You can search transactions in Square by:
1. Select Transactions on the navigation panel on the left hand side of the screen.
2. Select the relevant date/month in the top left.
3. Change the Card # drop-down to Note.
4. Enter the Receipt # from your MassageBook account and select enter.