It’s been a long-standing problem in Ivy that entering a string which was not on the list of candidates, but was a substring of one of the candidates, was non-trivial. You had to remember to press C-M-j instead of RET, and that requires some finger acrobatics.
Well, it’s no longer a problem. In one of the recent versions of Ivy, a new variable called ivy-use-selectable-prompt was introduced. With it, you can just press the up arrow when on the first candidate to select the contents of the prompt line. Very nice!