Well - now two IRS letters. Received a bill for $19,500 for later filling of my 5500-ez for 2021. Two really stupid mistakes by me:
1. Filled in the form online, signed it, then forgot to submit it which is a separate step.
2. Upon realizing this error a couple months later I filled the return before researching what options I had - I should have applied for voluntary relief and paid $500, but but by the time I learned of this option, I had already filled and no longer qualified.
The person I spoke to thought they might wave the penalty with a "I really tried - look at the timestamps in the system for this!" but now I get to find out.
ETA: Have sent in abatement request letter. If they don't go for it, I'll probably just pay (or set up a payment plan - the letter says only interest will accrue if I'm late with this payment, so I mean, why not try to pay $200 / month or whatever if they'll take it).