Is an increase paid to a person in exchange for completing a transaction, with the payer knowing that this person will pay a bribe to another party, considered a bribe that necessitates sin on the payer?

If you deputize someone to connect a phone line for your account without harming others, this deputization is permissible. If the agent oversteps and bribes an employee, the sin is solely upon him. However, if you deputize him for an act you know beforehand will be an injustice to others, such as prioritizing your application over those who came before you, then this deputization is not permissible, and both of you are partners in sin. The sin is compounded if you pay a bribe, and in that case, the agent does not deserve any payment. If the deputization was permissible and you disagreed on the payment, he is entitled to the customary wage. However, he is not permitted to take it if he completed the transaction through bribery. He must repent, as the Prophet, peace and blessings be upon him, said: "Allah curses the one who offers a bribe and the one who takes it."