That’s the business’ risk for sending those prepaid envelopes out. From the USPS site itself “[Moreover, when a BRM card or envelope is misused and affixed to a sealed item, the permit holder will be responsible for payment of the applicable Retail postage and per piece fee.]
DMM 505.1.4.8, “Labels,” states that in cases when a BRM card or envelope is misused as a BRM label, USPS® treats the item as waste.
BRM cards and envelopes are designed to be mailed as a First-Class Mail card, letter, or flat only, and not as a BRM label to be attached to other items.
That’s the business’ risk for sending those prepaid envelopes out. From the USPS site itself “[Moreover, when a BRM card or envelope is misused and affixed to a sealed item, the permit holder will be responsible for payment of the applicable Retail postage and per piece fee.]
But it also says
So I’m still a but fuzzy
Weird self-deprecating thing to say, and not sure how it relates, but best wishes with that!