Donate not working

[Kaeliah]

It works on my site... Did you put the symbol '$' in? If you did then don't, just put the amount only in, and see if that works.

Basically according to the code there are 4 reasons you would get that error.

The amount entered is invalid, meaning you added letters or symbols where only numbers are supposed to be.
You put in yourself as the receiver of the donation.
You did not put anyone in as the receiver of the donation.
You misspelled the receiver's name.