When using Magento 2 with Shiptheory, it's now possible to have more flexibility in the weight that is sent through to Shiptheory from Magento 2.
In the past, the weight pulled through was always the sum of your products' weights. This, of course, is still an option, but you can now choose to pull this from other fields. More specifically, Shipment Weight and Order Weight.
To select this, head into your Magento 2 settings page in Shiptheory and scroll down to the bottom to find "advanced settings":
If you then scroll down further, you will see an option to change this:
As you can see, you can select between the three options here. One thing to note, as mentioned in the image above, is that if you select Shipment Weight or Order Weight, but the field in the order is empty, then Shiptheory will fall back and use the sum of your product weights.
If you have any issues or questions there, please feel free to Contact Support.