If your business use percentage did not change after you converted it to a rental, then you should report the sale under the Rental Property.
The message about a variation in business use would apply if you used it (for example) 100% for business one year, but only 50% for another. If it was always a rental after conversion, this message would not apply.
Note that if you used the asset 100% for this rental business, enter total amounts in the sale section. If you had used the asset for any other purpose, you would then allocate the total amount to the percentage of use for this business. The prior history of this asset as your personal residence does not apply here.
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