@Rumo is right and if it’s still not clear what went wrong and how to fix it, here’s a quote from the above manual.
To create a cloze deletion note, select the Cloze note type, and type some text into the “Text” field.
This is because the front and back templates contain {{cloze:Text}} and Anki expects to find cloze deletions in the “Text” field, not in the “Back Extra” field.