SB should disclose why they were asking the OP for his KYC information. They should also clarify as to what basis they are saying that the OP "did not pass" KYC....
So the flag is basically invalid because the dispute is about 0.271 BTC, not 0.373 BTC as claimed in the OP. I could understand a small discrepancy but I don't think we should be supporting "written contract" flags overstated by 37%. There's probably more reason to oppose the flag than support it based on the amount alone, i.e. the claim is "at least partially false".
Most of the time, with mortgages and with rent, your lender or landlord will not accept less than the total amount due. A tenant or borrower offering a partial payment may be rejected, and this offer will not make a person owe a lower amount. The OP has not accepted a payment in the lower amount that SB is offering, and as such, he is still allegedly owed the full 0.373 BTC.