Personally, I think that a partial repayment would be reasonable even if Goat can afford the whole thing. The contract says "best effort" (...)
I think any court would find the terms of the contract insane enough to make the whole thing null and void.
And also that Goat owes Gurrty the full principal, if Gurrty can establish that he sent the money.
In a nutshell: If it can be established that you gave me a million dollars according to some completely insane contract, and the contract is found to be invalid... I don't get to keep the million.