1. The Mac is awake, the app is running, and library sharing is on
The library only exists while the app is running on an awake Mac. A closed window is fine: with library sharing on, the app keeps running in the menu bar. Check that it's there, and that the switch in the Sharing tab is on. If the Mac sleeps a lot, turning on Wake for network access in Energy settings keeps it reachable, or you can stop it sleeping while it's charging. Quitting and reopening the app also clears most post-sleep hiccups.
2. Both devices are on the same network
Look at the Wi-Fi name on the iPhone and make sure the Mac is on the same network. A Mac connected by Ethernet is fine, as long as it's plugged into the same router. If the iPhone is on cellular or its Wi-Fi is off, there is nothing for it to find.
3. The iPhone allowed Local Network access
iOS asks the first time an app wants to look for devices on your network, and Raza Photos and Raza Songs use it only to find your Mac. If you tapped Don't Allow, go to Settings → Privacy & Security → Local Network and switch the app back on.
4. The iPhone isn't on a guest network
Guest networks are separated from your main network on purpose, so a device on one can't see your Mac. That is the router doing its job, and it's also why visitors on guest Wi-Fi can't browse your library.
5. Both devices are on the same subnet
A second router, a mesh system or an extender running in router mode, or a powerline adapter can put devices on separate networks even though they share a Wi-Fi name. Compare the two IP addresses: on the iPhone, open Settings → Wi-Fi and tap the (i) next to your network; on the Mac, open System Settings → Network, choose your connection and open Details → TCP/IP. On most home networks the first three numbers match (for example 192.168.1.x). If they don't, the devices are on different networks and Bonjour can't cross between them.
6. The router isn't blocking device-to-device traffic
Look in your router's Wi-Fi settings for AP isolation, client isolation or wireless isolation, and turn it off for your main network. Some routers and mesh systems also filter or throttle multicast traffic, which is what Bonjour uses to announce your library. If discovery works on some devices and not others, or only on one Wi-Fi band, this is the usual reason.
7. A VPN or filter on the iPhone isn't in the way
Some VPN and content-filter apps send all of the phone's traffic through a tunnel, which can stop it reaching devices on your local network. Switch it off for a moment and reopen the app. If that fixes it, look for a setting in the VPN app that allows local network access.
For the technical: VLANs and multicast
Bonjour is multicast DNS (mDNS, RFC 6762), which is link-local by definition: routers don't forward it between networks. If your home uses VLANs, for example a separate one for smart-home devices, the announcement won't cross between them unless your router or a reflector relays mDNS. That isn't something the apps can change, and it's why we describe the network boundary as a property of the protocol and not of a setting. How discovery works →
It works at home but not away from home
That's the default. Your library is available everywhere in the house and nowhere outside it. If you want it to follow you, there's an optional, off-by-default way to do that. How remote access works →
Still stuck?
Email the developer. You'll hear back from a person, not a queue: razaphotos@outlook.com for Raza Photos, razamusic@outlook.com for Raza Songs. Tell us your macOS and iOS versions and which of the steps above you've already tried, and we can usually narrow it down quickly.