If orders are being sent from Cin7 to Shiptheory without a weight, or a weight of zero, you need to enable product weights in your Cin7 account.

How to enable the product weights in Cin7

  1. Log in to Cin72.
  2. Click on your username on the top right and click Settings
  3. Under the Products category, click Product Settings
  4. Change the Option Weight dropdown to Yes.

After following those steps there will be a new weight field available when editing a product. If all of the products in a Sales Order have weights associated with them I would expect the weight to be sent to Shiptheory correctly.