How do I add a subway station using iPad maps.me application?

I’m on vacation in Istanbul and found that the historic area map near Sirkeci is outdated. I thought I’ll be able to improve it. I went adding a hotel ( Askoc ) and succeeded, then tried to add a Sirkeci marmaray station near ex- Orient Express but failed to find an appropriate category. Then I went to the website but also failed to find a metro / subway station category. So, I decided to add just a point with no category but even with added checkin comment it refused to save because of inactive save button. What am I doing wrong?

See: http://wiki.openstreetmap.org/wiki/Proposed_features/Public_Transport

However such stations are potentially very complex. Also see http://wiki.openstreetmap.org/wiki/Tag:railway%3Dsubway_entrance

Thanks for links, many aspects are definitely too complicated for editing with iPad, but Imanaged to add the station in way similar to the nearest existing one.
Now couple more questions. As I mentioned, I’ve added a hotel and it is visible on both website and maps.me app I used as an editor for adding it. The subway station is now seen in website, but I’m not sure how do I download it to the maps.me. Now the third case: I’ve added a currency exchange point using the maps.me, the app seems to upload it but I don’t see it in website mode. So, my question is how (maybe how soon) these updates get in sync in app and web? Thanks in advance for your answer.

Updates to the OSM map (and website) take a bit longer with maps.me than with other editors (like JOSM). But in my tests the POI I added appeared within 5 minutes on the OSM map.
Be aware that not all POI or other objects are visible on the standard map! If you want to see POI, use OpenPoiMap.

The updates to the maps.me map itself take much longer! The maps are being used offline and are updated monthly, and you need to download the refreshed map yourself from within the app.

But there is a work-around to get daily updates:
http://www.openstreetmap.org/user/Zverik/diary/35658
but it is quite cumbersome!