Check here and try to enter a number higher than $5600.
I know this question might be oddly specific, but i have no idea why it would be such an odd number, and not just $5000.
The FEC raised contribution limits for the 2020 election cycle to $2,800 for each election period. The primary and general election each counts separately, so for both of those elections the maximum individual contribution someone can give to a single candidate adds up to $5,600. See also this announcement from OpenSecrets.org.
Because that's the legal limit. You can give $2,800 per election, so $5,600 would be a combined primary/general limit.