Unable to add work of music that score is based on

I get the usual prompt after setting the score to public when uploading to fill in the details of the work the score is based on, but since the composition isn't found in Musescore's list, I went to add a new composition. I get as far as filling in the details. but the "Add" button is unresponsive, as in, I click it and nothing happens. I'm using version 3.6, and I'm on Mac. Any and all help is greatly appreciated!