I found many apps fro redmine usage. But non of them connects to my openproject installation.
I try apps for android

• MyMine

And I try apps for ipad

• redminePro

I tried it with the api key and became an http 410 Error
I tried it with login and got an other error I can’t remember.

• Are there any clients that can be used?
• Are there any openproject configurations that must be done to use these redmine clients?
• Are there any plans to provide an own openproject mobile client?

Try this and let me know if it works.

http://www.arctickiwi.com/blog/mobile-enable-your-ruby-on-rails-site-for-small-screens

Thanks,
William Cornett,PMP
ExagoWeb Development Group
http://exagoweb.com