What is the ruling if the master appoints an agent in the city where the mukatab resides to receive the payment?

Supporting text

If the master explicitly authorized the agent to dissolve the contract upon the mukatab's refusal to pay, the agent may dissolve it, provided the agent's authority is proven by clear evidence (bayyinah) such that the mukatab is secure against the master later denying the agency. If such proof is absent, the mukatab is not obligated to pay the agent, and this constitutes a valid excuse preventing the master from dissolving the contract, because the mukatab cannot be certain that if he pays, the master will not later deny the agency and claim the amount from the mukatab, regardless of whether the master confirms or denies the agent's authority.