Building https://check.supply: the easiest way to mail a real paper check from your iPhone. Link your bank, type the amount, and we print + mail it for you — with optional certified or express USPS tracking

I built this same thing about 15-20 years ago, there was no plaid so I just had them input their routing and account info, I could print anything I wanted on the MICR line so I don't see why you need access to a user's bank account (seems intrusive to me). Also, at that time, I had trouble getting people to pay me even enough to cover postage so bravo to you if you have people paying you $7/check.

Really nice app design. For us outside the US, what is the use case for this? I don't think I've seen a paper check in over twenty years.