Some market-linked debentures are listed on an exchange debt segment and many, including the Edelweiss notes on this site, are issued unlisted. It is easy to read a listing as meaning you can sell whenever you like. In practice, secondary trading in these notes is thin to non-existent either way. There is rarely a buyer on the other side at the moment you want one.
Where a note is unlisted, the point is sharper still: there is no exchange to sell into at all, so an issuer buyback is the only route out. Check which one you are buying, and treat any listing as a regulatory and administrative feature rather than an exit route you can count on.