The call connects but nobody can hear anything

This half is usually simpler and almost always local. Check the volume during the call rather than before it: phones keep separate volume levels for the ringer, media and calls, and the call volume is only adjustable while a call is in progress. Pressing volume up on the home screen changes the ringer and does nothing for the call you are about to make.

Then check where the audio is going. A phone that is still paired with a car, a speaker or headphones in a drawer will happily route the call there, and the screen usually says so in small type. Turning Bluetooth off during the call moves the audio back to the earpiece immediately, which is both the diagnosis and the fix.

Silent mode does not mute call audio on either platform, so that is not it. What can mute it is a stuck earpiece speaker — if a previous call was on speakerphone and the audio only works on speaker now, the earpiece is the problem rather than the app. Compare with a normal phone call using the built-in dialler: if that is silent too, it is the phone.

Silence in both directions on a call that otherwise connected is the signature of a network that permitted the call setup and then blocked the audio. The two travel separately: the negotiation that sets up a call is a small exchange with our servers, while the audio itself flows as a stream of small packets, frequently on a different port range. A firewall that allows the first and blocks the second produces exactly this — a call that appears to work with nothing in it.

It is common on corporate and campus networks, on some hotel WiFi, and behind routers with restrictive default rules. The test takes one call: turn WiFi off, dial on mobile data, and see whether the audio appears. If it does, the network is the cause and the app is behaving correctly.

Where mobile data is not an option, the network's administrator can allow the traffic, but there is nothing to configure on the handset. A VPN sometimes routes around the block and sometimes makes it worse by adding latency; it is worth one test, not an afternoon.

Sound that is present but useless is a separate condition with separate causes, and it is worth naming so you do not chase the wrong thing. A long delay before the other person's voice arrives, words arriving in clumps, or audio that cuts in and out are symptoms of latency and packet loss rather than of a broken audio path.

Those are covered in choppy and robotic audio, which explains what causes them and what actually helps. The distinction matters because the fixes have almost nothing in common: silence is a permission or a firewall, and choppiness is a network under pressure.