Try going to the calendar on the app and changing it there.This seems to override MM.

3) What app docs will you ask for?

If the complaints are unfounded: Hopefully the threats/extortion was sent in the Airbnb app.

Advice NeededTLDR - Spend an additional $30k now to upgrade the sewer system on-site while the contractor is already mobilized or go with a sewer injection pump which is likely a viable solution the will last for years with proper maintenance. 

Or I wanted the lot behind my house so no one buys it and puts a mobile home on it. 

Every system you try will have flaws, or you may salivate over a feature that appears in other software.Some familiar names are mentioned frequently: Stessa, Apartments.com, RentRedi, TenantCloud, Innago, RentManager, Avail, Rentec Direct, Doorloop, etc.I recommend conducting thorough research on each app online to understand their offerings, pricing, etc.

and they even have an app.

Have you heard of Rent App and is that a good idea (instead of Venmo) and sufficient for tracking rent payments?

Much depends on what you give the CPA...........is it a shoebox full of paper or did you fill in their app?

By way of comparison, the same year I bought the lien on the 36 acres parcel of commercial land being discussed here at 16%, I bought a lien on a double wide mobile home affixed to a permanent foundation in some remote Arizona town, and I got that one at 0%.The bulk of the property is not in a flood zone.