Confirm it is really broken
First, rule out the stranger: ask via text chat whether they hear you, or test with a second device. If nobody hears you anywhere, the fault is on your end. If one stranger cannot hear you but others can, their setup is the problem, not yours.
The permission check
Go to Settings, Apps, Permissions, and confirm Microphone is set to Allow. This is the number one cause, and it often happens when the first-run prompt is dismissed too fast. The permissions guide shows exactly what each permission does in the Umingle APK.
The headset hijack
Unplug any wired earphones and test again. Some headsets, especially cheap ones with inline mics, seize the mic route on older phones and deliver silence. If unplugging fixes it, the headset was the whole story. Bluetooth headsets can do the same: disconnect them once as a test.
App-level resets
Force-stop the app, clear cache, and relaunch. If the mic works in your voice recorder app but not here after all this, you are looking at a rare app-level fault: reinstall the APK fresh from the install guide and retest. Persistent echo rather than silence is a different beast, covered in the echo fix guide.
