TLDR: don't trust anyone offering you a fixed rate of return, if it sounds too good to be true then it probably is. Great advice but very much over-complicated here.
A fixed return is possible if the creditor is absorving the risk.
Creditor runs risky investments using your money, but gives you fixed returns in exchange for lower yield. This is fine as long as there's oversight over liquidity to guarantee the fund manager didn't lose it all - it'd then become a ponzi.