In my first hand experience, I've seen several things that can cause this. One is that on some screens the program doesn't provide the clarity on the information being requested, that I think it should. Another is that there are screens where the clarity is provided, but users don't read the small print on the screen so they fully understand what is being asked for.
So in case you find it helpful, I'm providing the below information. In case it matters, if you only own 50% of the property, then business use of "your" 50% would still be 100% business use.
Rental Property Dates & Numbers That Matter.
Date of Conversion - If this was your primary residence or 2nd home before, then this date is the day AFTER you moved out, or the date you decided to lease the property – whichever is later.
In Service Date - This is the date a renter "could" have moved in. Usually, this date is the day you put the FOR RENT sign in the front yard.
Number of days Rented - the day count for this starts from the first day a renter was contracted to move in, and/or "could" have moved in. That would be your "in service" date or after if you were asked for that. Vacant periods between renters do not count for actual days rented. Please see IRS Publication927 page 17 at https://www.irs.gov/pub/irs-pdf/p527.pdf#en_US_2020_publink1000219175 Read the “Example” in the third column.
Days of Personal Use - This number will be a big fat ZERO. Read the screen. It's asking for the number of days *YOU* lived in the property AFTER you converted it to a rental. I seriously doubt (though it is possible) that you lived in the house (or space, if renting a part of your home) as your primary residence, 2nd home, or any other personal use reasons after you converted it to a rental.
Business Use Percentage. 100%. I'll put that in words so there's no doubt I didn't make a typo here. One Hundred Percent. After you converted this property or space to rental use, it was one hundred percent business use. What you used it for prior to the date of conversion doesn't count.
