More detail would help but the following may be useful.
You can't leave feedback for transactions from more than 60 days ago.
You can't ever leave negative feedback for buyers.
If you bought from some business sellers, you can't leave negative feedback until 7 days have passed. That is so you can give the seller time to sort the issue out for you.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)
