Fixing discrepancies with tracking numbers between Squarespace and Shipstation/Stamps.com

Site URL: https://www.thereactoriscritical.com/

So, I've noticed this same issue before with letters, but I'm finding the same deal pop up way more often now that I've started shipping one of our new items with large flat envelopes, and a lot more people are asking what's going on.

Whenever I try to ship an order as either a First Class envelope or First Class large flat envelope, Shipstation/Stamps.com doesn't provide us a tracking number for it. Squarespace, however, does, and I don't know how or where it's getting it, and the number it provides to customers doesn't actually work when they look it up. We've had a lot of people write to us since to ask why they can't track their order.

I'm wondering if there's a way to modify the site's Commerce or Shipping settings so that it stops providing tracking numbers for these particular orders. If I can't do that... what else might I try to stop confusing customers with information they can't use?