Error Syncing Payment #INV 3552:  - : 
  "Errors": [
      "Name": "ValidationError",
      "Message": "ReceivePaymentEvent_LineSaleEventDoesNotBelongToCard",
      "AdditionalDetails": "Lines:(ReceivePaymentEvent)",
      "ErrorCode": 4625,
      "Severity": "Error",
      "LearnMore": null
  "Information": "Warning, error messages have not been finalised in this release and may change"

This indicates that the customer in MechanicDesk and MYOB does not match. For example

in MD the customer of the invoice is A, but in MYOB it is B.

when MD sync the payment of the invoice, MYOB rejects the payment, saying payment from customer A cannot apply to invoice from customer B.

we will need to open both invoices from both system and adjust so they bills to the same customer. Also adjust the payment customer (if it is also incorrect) then start a quick sync.