Methods, apparatus, systems, devices, and computer program products directed to enhancements to proximity-based services (ProSe) direct discovery are provided. Among the methods is a method that may be implemented in a proximity services (ProSe) function and that may include receiving a discovery request message including a ProSe application identifier; determining whether or not the ProSe function can retrieve a valid ProSe application code corresponding to the ProSe application identifier; and transmitting a reject-type discovery response message conditioned on the determining that a valid ProSe application code is not available to the ProSe function.