@Rodrigo717 This is just a discussion forum for hosts and guests, not Airbnb customer service. Ways to contact CS are on the first page of this Help forum. Just call them and tell them the host is asking for cash payment. Hopefully you and the host have been communicating through Airbnb messaging, so Airbnb can see the exchange.
Yes, asking for cash is against Airbnb TOS, but I think some commercial listings are allowed to take a cash security deposit. Only Airbnb can tell you if it's allowed for this listing, and if it's not, they will probably contact the host to tell them they can't ask this of you.