When processing orders you might come across the "6003 The COMMERCIAL_INVOICE requires an electronic SIGNATURE" error.
This error is shown when the ETD (Electronic Trade Documents) usage has not been enabled for your account, or if so, it has not been properly set up in techSHIP.
To fix this issue you need to complete FedEx's requirements to use ETDs with your account as described here: https://www.fedex.com/en-us/electronic-trade-documents/enable.html
You cannot activate electronic trade documents without uploading the letterhead and signature images.
Once done and approved by FedEx, follow the steps below to upload your Electronic Trade Documents images and assign them as indicated here: How to upload and use FedEx Electronic Signature images for ETD [Step-by-step guide].
Once corrected, this error message will not be displayed and the orders will be able to process correctly.