There is obviously more to the situation than posed but I dont think anyone cares about some long drawn out story and drama. So I'll try to just stick to the pertinent details:
Person A is owed by Person B(17k) and they each agree on the amount owed and never has there been any ghosting, arguments, or bad blood between the two, both in regards to this debt and their relationship as a whole. They have done a variety of deals and were more or less friends.

The two parties agree to a repayment plan with a fixed amount to be paid each month. After they effectively 'shake' on the deal, Person A immediately asks for the first payment and person B says he fully intends to pay but should have the time interval they agreed on to be able to make the first payment. Person A deems this unacceptable and now says to repay the balance in full by the following day or he will publicly blast him as a scammer and ruin his reputation. Person B is unable to maintain a civil tone and the two argue. Person B tries to get them to arbitrate the situation and person A declines.

The following day person A posts on a scammer group calling out person B and messages numerous ppl to not do business with person B. Person B is inundated with messages and is added to the list of scammers, and his reputation takes a definite hit. Person B feels its not right that person A ignored their clearly agreed upon payment plan as he never missed payment or showed signs he wasnt willing to pay. Person A will not remove post and feels what he did was okay.

Person A feels person B should pay the agreed upon payment terms but that the post should remain up. Person B still wants to repay debt, but doesn't feel its right that their deal can be ignored and the post remains up/he remains on list and that he still has to keep the terms they agreed to.

So the questions;
- in repayment plans is there an obligation on the person owed the money to keep the matter private(in the sense its not publicly posted) so long as the terms are being met?
-If the answer to the first question is yes, what happens when the terms are ignored like they were in this situation? Person B still wants to repay debt, but does believe at a minimum post/name on scam list should be removed.
-When a repayment plan is made is the first payment assumed to be immediately paid the day the plan is made or does the person have whatever time interval is decided to make the first payment?
-How should each party proceed from this point?

Usually one of the two geniuses realizes that a repayment plan without a repayment schedule is not much of a plan. Heck, a contract that does not stipulate whether payments start at [$agreement_time] or at [$agreement_time + $interval] also by definition does not guarantee that a payment is due at [$agreement_time + $interval]. The question of when repayments start is left completely unanswered.

But if neither of them realize that they forgot a schedule? Then I'd say it should default to [$agreement_time + $interval]. They are effectively treating it as a loan kickoff at that point, and it doesn't make sense for the borrower to immediately pay back part of the amount he is borrowing.

The reason why there isn't a clear default here is because most repayment plans don't get to the handshake without a schedule.

This seems to have escalated quickly from "no bad blood" and "more or less friends". My read is that Person A has already given Person B a lot of leeway and has had enough. Which person are you?

no there was a very -set in stone amount to be paid each month, which I thought naturally meant first payment must be made before end of time interval. It seemed quite obvious to me but really was what set the other person off.

Im person B, but I left out a lot of the context and events leading up to this specific repayment plan. We actually had two previous plans that person A would be operating under for a few months then out of nowhere demand a new plan. Hes showing a history of making deals but not honoring them, and is new to the industry as of quarantine. ---