The error stems from the fact that my EFIN is not registered to e-file 1040 Modernized e-file with the IRS.
Then it sounds like you did not check off the box 1040 for the types of return you will be submitting with the EFIN when you applied for it. You may like to check your Application Summary and see that 1040 is listed under Provider Option(s), if you had a copy of that printed out. Otherwise, log into your e-services account and check what you have been authorized as an ERO.
Still an AllStar