The error "The Shipper's shipper number cannot be used for this shipment" typically means the UPS account has been suspended--usually due to a billing problem. There may be an outstanding balance or the credit card may have expired. There is some kind of hold on the account.
Another common reason we see this error is that someone changed the ups.com password on your UPS account and didn't alert ShipLeap support, which will usually lock your account for 24 hours
There is a similar error message that you may see. "The shipper cannot use the provided UPS account number as the payment method."
The account holder must call UPS at 1-800-742-5877 (1-800-PICK-UPS) and ask "what kind of hold has been placed on my account" because an error is displayed while shipping using the UPS API. See below.
When speaking with Tier 1 Support on the phone, tell them very clearly:
"I am making an XML API request and receiving back error 120121. The error message is 'The Shippers shipper number cannot be used for the shipment'. Can you verify that my account is in good standing for use with the XML Shipping API?"
When submitting the web form to UPS API Support, send text similar to the following:
"My UPS Account number is [######], and my UPS.com username is [xxxxxxxx]. I am making an XML API request and receiving back error 120121. The error message is 'The Shippers shipper number cannot be used for the shipment'. I understand this means there is an issue with my account. Can you help me clear up any holds or other issues with the account that are preventing me from shipping with the XML API?
If you still can't use the UPS account, wait the indicated amount of time or 24 hours for the hold to be released before trying to use ShipLeap again.