Is it permissible to take a "Sa'i" (brokerage/facilitation) fee when agreeing upon a financing amount, a fixed annual interest rate, and a one-time insurance payment, knowing that the commission is only from the principal amount?

It is not permissible to mediate in a financing transaction that is a loan with a stipulated increase, and the commission for this mediation is forbidden because it is usury. Usury is one of the gravest major sins, and it is not permissible to assist in it. As stated in the Hadith: "The Messenger of Allah, peace and blessings be upon him, cursed the one who consumes usury, the one who feeds it, its scribe, and its two witnesses, and he said: 'They are all equal [in sin].'"