Thank you h_lamia, for your reply, and info.
Could the sound level reaching the headphones be too low ?
You might want to try adjusting the audio levels ?
Adjust the audio settings on iPhone
https://support.apple.com/en-au/guide/iphone/iph3e2e2cdc/ios
or
Customize the headphone audio levels on your iPhone
https://support.apple.com/en-us/HT211218
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Or
Wondering if this is what you are experiencing:
After you plug any headphones into your iOS device,
sound plays from your device's speakers instead of the headphones ?
If your iPhone 7 won't recognize your headphones,
seems you would need to get help from Apple.
https://support.apple.com/en-us/HT201232
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You might want / need to visit an Apple Store:
a Genius Bar reservation is recommended:
How to make a Genius Bar reservation at your favourite Apple Store, and get help from an Apple expert.
(Change the country at the top to suit, if needed)
Genius Bar Reservation and Apple Support Options - Apple
Or
There is a "Get support" link to Apple at top right on this discussion page.
OR
Apple phone numbers around the world
https://support.apple.com/en-us/HT201232
All the best!