Hello there, @jennifer62.
I know how beneficial this feature would be if we're able to place a pay now button when customers receive their invoices. Currently, this feature is unavailable because the Merchant Services Center hasn't fully integrated with QBDT for Mac yet.
For more details, you can check this article: Turn on online payments in QuickBooks Desktop for Mac.
In the meantime, I'll add this link as your guide in using QBDT for Mac: QBDT for Mac 2020 User's Guide.
Feel free to comment below if you need further assistance. I'll be around to help. Have a great weekend!