USPS error: ‘Failed to convert parameter value from a Int32 to a Byte’

This error usually comes up when trying to create an international shipping label via USPS. This means that at least one of the customs decalarations line items has a quantity of more than 255.

When this happens, what you need to do is simply go and distribute the quantity on more line items, so that none of them exceeds this criteria.

Once you make this change, everything should go back to normal.