Is it permissible to invoke blessings upon the Prophet (peace be upon him) once before and after a group of supplications, or must it be repeated before and after each individual supplication for the supplication to be answered?

There is no harm in limiting oneself to sending blessings upon the Prophet, peace and blessings be upon him, after finishing supplications, for every supplication is veiled until blessings are sent upon Muhammad, peace and blessings be upon him. It is permissible for the blessings to be delayed in time from the supplication. However, it is better for the supplicant to begin by sending blessings upon the Prophet, peace and blessings be upon him, as it is stated in the Hadith: "When one of you prays, let him begin by praising Allah and extolling Him, then let him send blessings upon the Prophet, peace and blessings be upon him, and then supplicate for whatever he wishes."

It is also legislated to send blessings between supplications and then conclude with them. There are three levels for this: to send blessings upon him before the supplication and after praising Allah, or to send blessings upon him at the beginning, middle, and end of the supplication, or to send blessings upon him at the beginning and end, placing one's need in between. The supplication is suspended between heaven and earth, and nothing ascends from it until blessings are sent upon the Prophet, peace and blessings be upon him.