A seller-financed mortgage is also known as an Installment Sale and reported on Form 6252 of your return.  To report this sale in TurboTax, you will need to upgrade to TurboTax Premium Online Edition.  TurboTax Free Edition does not support Form 6252. 

Please use the following instruction for reporting this sale on your return. https://ttlc.intuit.com/replies/5639251