My On-time shipping & tracking is really low. We sell postcards with a regular stamp. USPS will not provide tracking number with a stamp. How we can fix that?
You need to send with tracking. You are in the US so have access to the not-tracked-but-counted-as-tracked letter label on Etsy. Perhaps use those.
buy an etsy letter rate label.
https://help.etsy.com/hc/en-gb/articles/360039466434-How-to-Deliver-First-Class-Large-Envelopes-Flat...
