Are paid posts not eligible for support?

They are eligible. All publicly published posts on POSTYPE, including paid posts, can receive support.

When purchasing a post, you can adjust the price to send a higher amount to the creator. Any extra amount you pay is recorded separately as support.

After purchasing a post, a support box appears at the bottom of the post, and you can send support starting from 100 KRW, in increments of 10 KRW.