SKULabs offers third-party billing for shipping carriers connected through EasyPost. To start using third-party billing, contact SKULabs support and request for this feature to be enabled for your account.
After connecting the new billing account, you can then choose which account to bill with during shipment by using the Billing dropdown in the ship window.
Automatically choose a billing account using a shipping rule
Optionally, you can create a shipping rule that automatically selects the billing account for you when shipping.
After connecting your third-party accounts, configure a shipping rule at settings > shipping > rules by choosing the criteria about an order to target and using Set Third-Party Billing Account as the shipping rule's action.
Please contact SKULabs support for more information or if you would like assistance.