It has been a while since I’ve had to use it, but when using PayPal shipping (USPS), have done electronic customs declarations and electronic invoice where I put in the quantity, description, weight, HSTS code, value, etc and had no trouble with. It seems to me two copies went in the external pouch and I put a third inside the box for good measure. It seems to help if their job is actually harder than taking the easy way if every piece of information they could want is readily accessible without opening the package.

Going the other direction, I remember a fun transaction where FedEx lost an e-cal module coming from Mexico to me in the US … after it went through customs. I raised a real stink firm and polite at first and ultimately after sending them a photograph and description of what they were looking for and conveying the sense that they really wanted to find it rather than pay a claim for loss, 13 hours later it was found, and injected into their system as an overnight and I got it the next morning.