"Reason for sale" vs "Reason for selling"

[Zillah]

Hi

Which one is more appropriate should I say :

The reason for sale this car downsizing to a smaller car

Or

The reason for selling this car downsizing to a smaller car

Thanks

[Vietanhpham_Winter]

Only selling is acceptable as you say sell the car not sale the car. Sale is simply a noun while you need a verb in that position and selling is a gerund which has functions as a noun but can play the role as a verb after a preposition or a phrasal verb(except to and combinations with it).
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[Jamie (K)]

Both of the sentences are incorrect, because they both lack a verb.

If you insert a verb, the one that is correct would be the sentence with "selling".

The reason for selling this car is (that I am) downsizing to a smaller one.