Does accepting cryptocurrency as payment classify a US company as an MSB under FinCEN?

Most likely not. If the company that is receiving the cryptocurrency &/or stable coin as payment, is also the company that is the merchant on record, then most likely, the activity is not an MSB (money services business) related activity, as defined by FinCEN.

An easy tell is if you are offering some kind of a banking service or handling money/payments as an intermediary, meaning you are neither the originator of the transaction, and neither the end beneficiary.

If you’re not a financial intermediary, there is a good chance you are not an MSB for accepting crypto/stable coins.

However, the most important thing here is to see the intent, transaction set and flow of funds to offer a proper opinion.

Needless to say, IANAL.