The last time I tried to send one out, the envelope was sent back to me saying it didn't meet the weight requirements, which made little sense to me because I've mailed a single Yugioh card to my cousin before with zero issue.
Then once I tried to send out a small manila envelope with some bubble wrap and an envelope only for it to be sent back to me again. This time it said the dimensions did not meet standards.
Postage was fine.
Thank you for your help.
Still not an adventuring biologist, dang it.