Some old posts were having a tier which costed $5 in past.
Then I removed this tier and created a new one costing $3.
SubscribeStar automatically made old posts cost $25 after removal of $5 tier, and I forgot to update around 6 old posts.
Thanks to this person on screencap, I did finally notice this, my bad.
In the future however, know that you can always message me with questions and I will reply as soon as I can!