When a payment is processed via the Square integration in your MassageBook account, MassageBook sends over 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 "Not" using the MassageBook Receipt number.
You can search transactions in Square by the Note.
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.