Most likely the reason is that Google Places API did not recognise the city.
The City field uses Autocomplete from Google Places. You should allow it to do so. You can start typing the name of the city and then select from drop down list the correct suggestion. Once the city is selected, the Continue button will be lit.
This ensures map based search queries are targeted to right location. If Google can not find the city, you can not complete the listing. In that case try different spelling or location nearby which is recognised by Google Places.