This error (Ship Web Service Error - Hard120100: Missing or invalid shipper number) from UPS typically occurs when the account number on the connection in Mintsoft is incorrect.
To resolve this issue, please follow the steps below:
Verify the account number:
Within Mintsoft, click Connect then Courier Integrations.
Next, click UPS.
Locate the affected UPS connection and click Edit.
Ensure the account number is correct.
Update the connection:
If the account number is incorrect, amend it.
Click Update to save the changes.
By following these steps, you should be able to resolve the error.