Hi,

This error usually means Odoo can’t calculate the total shipping weight, even if your products have weights set. While you may have added weights on the product pages (including variants), Odoo needs the weight to be present on the Delivery Order’s move lines. Specifically, go to the Delivery Order, open the Operations or Detailed Operations tab, and check the Weight field for each item. If any of them is blank or zero, Odoo won't be able to fetch shipping rates from EasyPost and will show this error. Odoo doesn’t always auto-fill the weight from the product, so you may need to enter it manually to automate it. Once the weights are properly set in the Delivery Order, the shipping estimation should work as expected.

Hope it helps.