My start up received an offer of $1,000,000.00 debt with 20% return. I am not sure if I should accept it or not, the investor is from outside the US which is little weird to me.
It depends on many factors. Are they willing to do it as a convertible note? If you're early stage the debt will be a burden if you don't have revenues in short order to repay it. 20% is extremely high and if you can't repay in revenues it could bankrupt you.
Investors outside the U.S. Are not weird at all, in fact often very smart investors. But you have to get to know them first.
In sum: how badly do you need the capital and do you think you can repay before it's due? If not you'll need to set repayment terms in case you don't hit your revenues. Just don't get stuck working to repay debt.