My original 2017 1120s was accepted but I need to amend it. I followed the prompts to file an amended return, but I get "not eligible for e-filing"

I filed a 2017 1120s but I need to amend it. The original has been "accepted".  I clicked on amend a return, picked the return to amend, corrected it, checked "yes" that I was amending a return, but when it was time to file, it keeps telling me "not eligible for e-filing".  What am I missing?