I have tried printing an Endicia (USPS) shipping label and am seeing an error returned:
BuyCredit: String or binary data would be truncated. The statement has been terminated
This error is being returned when Allow Auto Postage Purchase is enabled in Linnworks.net > Shipping > Integrations > Endicia Label Server (USPS) > Config, but the values for Auto Purchase Amount and Auto Purchase Trigger Amount have not been set correctly.
Please add valid values for Auto Purchase Amount and Auto Purchase Trigger Amount for Linnworks to increase the balance automatically in case it will go too low.
Endicia Label Server documentation