QBWC1012: Authentication failed due to the following error message. Server was unable to process request.

QBWC1012: Authentication failed due to the following error message. Server was unable to process request. You have synced more sales than your license key allows. Go to connexforquickbooks.com/log for more information"

This happens when you're using a trial version of a third party app and you've exceeded your trial.

What you can do?

1. Update Web Connector to the latest version.

2. Update your License Key. 

Note: If you still get this error, reach out to Intuit Support.

Reference: https://quickbooks.intuit.com/learn-support/en-us/set-up-payments/fix-common-web-connector-errors/00/203305