What is the ruling on adding variable fees when depositing or withdrawing an amount of money in the same currency in an electronic wallet?

It is permissible, according to Islamic law, to charge fees for depositing money into an electronic wallet. This is considered a wage for the service provided, which includes safeguarding the money, depositing it, or transferring it. The basic principle for a wage is that it should be a fixed, known amount. It is permissible for it to be a percentage, or a variable wage that increases by a known percentage for subsequent periods. However, the wage for the first period must be a specified, known amount. Furthermore, the precise indicator for determining the wage in subsequent periods must be tied to a known standard that leaves no room for dispute, and a maximum and minimum limit must be set for it.