In some cases, you may have 2 accounts from the same Carrier.
For example, you may two DPD accounts. The first DPD account may be for heavy items and the second may be for lighter items. Shiptheory's rules can work with both of your DPD accounts.
This is true for all carriers Shiptheory supports.
If you would like to use 2 accounts from the same carrier, please get in contact with support.