Trouble Shooting

Check if your device is running Android 4.4.x. If so, I recommend that you undo the purchase in Google Play. If you're brave, you might want to check out how to run on Android 4.4
Check time settings of your device: if your device clock is wrong in excess of a few minutes, the tunnel will silently fail. Cross-check the time zone setting (having the clock at the correct local time, but wrong time zone is equivalent to a clock setting n hours wrong).
The problem might be with DNS lookup not working (some provider's DNS servers seem to block requests for AAAA records): call up settings, route settings and activate the option "Use Google DNS servers".
Stop and start the tunnels
Retest IPv6 connectivity, e.g. at http://test-ipv6.com/

You would see a warning at http://test-ipv6.com/ in these cases:

IPv6 connections work, but connections using DNS names do not use IPv6. For some reason, your browser or your OS is not doing IPv6 DNS 'AAAA' lookups

stop any running tunnel using the stop icon in the action bar
call up the extended menu via the three dots in the action bar (or the dedicated menu key of your device in case it has one)
select the „Settings“ entry
swipe down to route settings and activate the option to use public DNS servers
switch back to the main screen (via the left arrow in the action bar)
start the tunnel again using the „play“ icon in the action bar.

A notification will be available with additional information, please check this.
Your account usually has more than one tunnel enabled, you have to select the one that should be used. The tunnels will be listed on the start page, the selected one is highlighted with a tick.
Call up "subscription" from the menu; this will update your subscription information, plus information if the subscription is expired. (this is not relevant if you run your own server)
If running your own server — you would know if you do — also check the following:
- Cross-check that you're using the correct user name and password for your server
- Cross-check that you didn't misspell your servers hostname under the hostname setting.
- Cross-check that your (IPv4) internet connection is functional.

Probably you were using an AYIYA tunnel at SixXS.net. They stopped their services at this date exactly.

It's easy, you can cancel your subscription even when IPv6Droid is no longer available (e.g. because you switched to a new mobile):

Call up Google Play on any of your Android devices you're using with the Google account that runs the subscription (alternatively, call https://play.google.com from a browser, then login to that Google account; password is required)
If the side menu on the left hand side is not visible, tap the menu symbol (three horizontal lines) showing within the search bar
Tap/click on the menu item "my subscriptions"
Here you see all your subscriptions. Cancel those you do not require anymore.
You will be able to use your tunnels until the end of the paid period. This does not affect subscription cancellation, i.e. is safe to do.

Please send an e-mail to support@flying-snail.de. Please include, as far as possible, the following information:

as much detail on the problem and its context as possible, but do NOT include personal data, passwords, credit card details or other sensitive information
a screenshot of the disturbed dialogue or 3rd party app (remember to erase sensitive information if applicable)
a screenshot of IPv6Droids statistics page
in case IPv6Droid reports the tunnel as running, call https://test-ipv6.com, wait for the tests to complete and include a screenshot of the result

IPv6Droid by Flying Snail

Provide feedback