The phone has served you well for 4 years but I assume the battery may not be holding up as well now.
This forum isn't a buying and selling site instead it's a peer to peer help forum so your going to need to use a specific site or Highstreet Store that buys and sells phones to conduct your intended business.
Please be careful where you share your personal information too.
I wish you all the best with this and hope you end up with your next phone of choice @Mantera
Current Phone ~
Samsung Note 20 Ultra 5G SM-N9860_256Gb SnapDragon 865+
Samsung One Ui 2.5/ Android 10.