An application error has occurred while processing your request when syncing the payments

The error will come when you Updating the payments from salesforce to QucikbooksOnline.

Reason:

The payment which is already inserted through DBSync and having the Payment ID value in salesforce, but some omne deleted that payment in QBOE and you trying to update the same payment in Quickbooks. In that case you get that error.

Below is the detailed Error.

<BatchItemResponse bId="1">

        <Fault type="SystemFault">

            <Error code="10000" element="SystemFailureError">

                <Message>An application error has occurred while processing your            request</Message>

                <Detail>System Failure Error: java.lang.NumberFormatException: For input string: &quot;&quot;</Detail>

            </Error>

        </Fault>

    </BatchItemResponse>

Solution:

Delete the Payment ID in salesforce which is stored in the DBsync field and re-run the sync payment, it will resolve your issue.