All perfect praise be to Allah the Lord of the Worlds. May Allah`s peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Based on the above question, the owner of the e-wallet is an agent who pays different bills or transfers money upon direct request of clients who pay him directly, even before he pays that sum via the e-wallet. Here, the general rule is that it is permissible for an agent to get a known wage-a lump sum or a percentage-from the client. However, if the client didn`t pay the agent directly, then this is a form of agency and loan, so, in this case, the agent isn`t allowed to charge a commission so as to avoid falling into Riba (usury/interest).
In conclusion, it is permissible for an agent to get a known wage from the client upon payment of bills or money transfer if the client paid the agent upon conducting the transaction via the e-wallet or prior to that. And Allah the Almighty knows best.