Logistics of Presidential Debates and Agreements/Contracts

I've never worked on a campaign. I would imagine there is a contract which both parties agree to certain standards, moderators, times, etc.

What is Trump's push for ear checks or Biden's push for breaks? Isn't this already decided and agreed upon? Is there a breach of contract claim or clause that requires payment from one campaign to the other if someone chooses not to debate.

I would imagine it would include a clause that if someone withdraws from the debate for COVID 19 reasons, there would have to be some proof of some kind.