AGI (MAGI) is only relevant to the threshold above which you are ineligible to make a Roth IRA contribution. Assuming that you are not married filing separately, you are far below that threshold and AGI is therefore irrelevant. Provided you have compensation, you can make a Roth IRA contribution.
Assuming that you are an eligible individual, your Roth IRA contribution is limited to your compensation. The SECURE Act made certain taxable non-tuition fellowship stipends be considered to be compensation for the purpose of an IRA. Generally this would include the amount on line 1 of Form 1040 with the SCH notation.
