A buyback obligation (also known as a buyback guarantee) is an obligation made by a lending company to the investor to buy back the loan (full principal plus interest) in case the loan defaults or reaches certain delay days. This is usually 60+ days delayed but it may differ by lending companies and loan marketplaces).
Because of buyback obligations, it is that the final risk of your consumer loan investment lies in the ability of the lending company to cover its buyback obligations towards you.
The buyback obligation does not, however, guarantee that your loans will always be repaid. In case a lending company defaults, it is very likely that the obligation will not be fulfilled and some of your funds might get lost.