Is the available balance from a monthly program, on which a fixed 5% administrative fee is paid in advance, considered to be in the same category as money on which interest is impermissible, knowing that this balance can only be used with merchants contracted with the program?

The transaction mentioned is a usurious loan and is forbidden, whether the borrowing is of money or other things. As long as an increase is stipulated in it, it is forbidden usury. Naming this interest "administrative fees" is a trick to circumvent what is forbidden. Muslims have unanimously agreed on the prohibition of any loan in which an increase is stipulated.