On smartphone, i cant get seller mode; there isn’t the icon to active it (except pc version)
For me, it’s the first toggle button if I go into the bottom right menu where other options like “Post a Request” and “Manage Requests” are present too.
Click on your Profile button (in the lower right corner of your app).
Just below your profile picture in that section, there’s a button to switch between seller and buyer mode.
Hope this helps.
Did you update the app to the latest version?