Land contract properties owe tax on full sale price?

[Cathy Malmrose]

I sold off a chunk of my portfolio in 2021 due to a heart attack (needed to slow down). I thought I would pay on the proceeds as the money came in, not the full sale price before any money had actually been paid on the property. For example, I sold three of the houses in a bundle for $650k. I did not get $650. I got about $1k at the closing table because of a small downpayment and commissions. My 1099-S from the title company shows I got the full sale price... I'm confused. How can I owe taxes on money I haven't even received?