This is probably a duplicate bug.
When we display a minimum amount error, do all of the following:
a) Use very exact language to explain that you need to increase the amount
b) Say exactly what that minimum amount is,
c) Provide a button or link that populates your donation with this minimum amount.
It would be polite to also explain *why* we have a minimum amount, using some wording that doesn't pull our vendors' pants down wrt. our contractual processing fees.