This was a change to PayPal's acceptable use policy which came out last June:
PayPal commercial users will have to agree to a $2,500 PayPal fine if they break the PayPal acceptable use policy from June 2020
tamebay.com
From their Acceptable Use Policy page:
Violation of this Acceptable Use Policy constitutes a violation of the PayPal User Agreement and may subject you to damages, including liquidated damages of $2,500.00 U.S. dollars per violation, which may be debited directly from your PayPal account(s) as outlined in the User Agreement (see “Restricted Activities and Holds” section of the PayPal User Agreement).
If you're going to fight this in court, then the battle shouldn't revolve around whether or not you agreed to the policy itself, per se, but rather to attack the part which says "...may subject you to damages..."
In other words, they would have to show where your violation actually caused them to suffer damages which required $2,500 per violation.