Android App problem

Hi.I’ve been using WordPress on our Scouts website without any problems for a few years but recently I noticed the WordPress Android App was not uploading my posts to the web page.
As nothing on the server has changed, I decided the best course was to uninstall the app. I reinstalled it but when it asked for the URL of the wordpress site, I got the message:

Couldn’t connect. We received a 403 error when trying to access your site XMLRPC endpoint. The app needs that in order to communicate with this problem.

After trawling through the web, most consensus says the fault lies with my domain server blocking wordpress but they have been very helpful in investigating this and found no blocks in place.
I’d like to stress the actual WordPress blog is working perfectly well. I can add (via the browser), delete, comment etc. etc. with no issues. It is just the ability to upload to the server via the Android app. I have definitely got the latest versions installed and there are no plugins active.

I am not a WordPress expert so an uninstall of the WP server is not on the cards. I don’t think I’d be able to get it going. But I can follow instructions if anyone has any suggestions.

The page I need help with: [log in to see the link]