Why don't my friends hear me?

In Fortnite nobody can hear me even though I have an open microphone plugged in a headset with a microphone.

Google times microphone test. If you can't hear yourself there, your microphone is not activated at all.

Then go to your sound settings and see which microphone is set there and try around there a bit.

Is micro, output device, with settings?

Does the mitkofon work? In Windows you can test this with the audio decoder.

Change the issue and see if they can hear you at one of the issues.

Otherwise use Discord.

Output = output. No microphone is input logically white.