We're you previously playing Spotify from your account on another device (your PC for example) when you plugged in the headphone adapter? In that case plugging the wired headphone adapter causes Spotify to shift playback to the phone instead.
If Spotify wasn't running on another device prior to plugging in the headphone adapter, please share a short screen recording which shows the app's behavior in action, so we can take a closer look. Feel free to also share the following:
The version of Spotify on your phone.
The troubleshooting you've tried so far so we avoid repeating the steps.
We'll be on the lookout for your reply.
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