How can we tell between a legitimate service fee and Riba? When a person’s phone’s credit runs out, he can request a top-up from the provider. However, there is a condition that a fee for topping up will be paid in addition to the amount. Is this a Riba (interest) arrangement?

Question

A service charge differs from Riba in that the former is paid for a service rendered, whilst the latter (Riba) is a payment for no service at all. The definition of service is any service that is considered as legal under Shariah. Top-ups might be considered a legitimate service for which a fee is levied.