Etsy,
If I ship two international orders from the same customer in one package and create one shipping label, I am unable to mark the second order 'complete' and include a tracking number.
If I ship an order as a letter to save a customer the high shipping cost, I have no way to mark the order 'complete' and include a tracking number because there isn't one. Also Etsy does not have a way to mark a letter as non-machinable for an additional fee and therefore I must go to the post office and purchase the postage.
Etsy has never had a non-machinable letter rate, which makes no sense. I've never had a problem combining two orders in one package with the same tracking number, however. I'm not sure why you wouldn't be able to do that.
@CaityAshBadashery: You have to manually mark the additional order(s) as complete and be sure to include the same shipped date, shipping company, and tracking number on all of the orders that in the single shipment. https://help.etsy.com/hc/en-us/articles/115015774228-How-to-Add-Tracking-and-Complete-an-Order-?segm... might help you.
But if they’re using stamped mail, which is what letter mail is, there’s no way to track it.
Have you tried using the flat option? I believe that’s what a non machinable letter is. I ship my stickers with the letter option and the tracking isn’t that good, but it’s cheap and no one will want to pay more than the price of a sticker to get it.