No, I do not know what the reason is, but, I successfully joined the program. The button to lock the story before publication is ghosted and I am unable to click on it. The Medium help desk told me some publications aren’t approved to participate in the partnership program, but, I never submitted the story to a publication. The issue remains unresolved. It is frustrating. I would like to participate in the program, but, maybe Medium isn’t the right venue for me. It certainly isn’t very encouraging.