The program doesn’t accept multiple answers at the same time. Just choose one. For some things, with dozens of meanings or readings, you wouldn’t want to be entering them all.
Regarding “to enter” being wrong, you can try installing the override script, which would let you change an answer from being wrong. Just try not to abuse it.
なな is the kunyomi. WaniKani doesn’t teach the onyomi and the kunyomi at the same time. You’ll learn other readings during the vocabulary lessons as they are applicable. But those two are pretty interchangeable in some circumstances.