How to upgrade to Avast Moblie Security Pro?

“Next” button is not responding.

Must be a language specific problem.
I had no problems in the English version.
I have passed this along to the developers.

@bob3160, thanks.

Hi, are you in a country, which could be blocking Google Play Services (e.g. China)? Unfortunately, you cannot buy Pro from any of these countries.

Hello Tereza V., I do come from China Hong Kong SAR, but under the 1country 2 system policy, this should not be the cause.
Besides, my sony phone does not have this problem.
The device which is in trouble is HTC Nexus 9.

Try to clear the Google Play and Google Play Services data (device Settings > Applications > Google Play > Clear data and Clear cache).

If it doesn’t help, try this:
https://support.google.com/googleplay/answer/1267137?co=GENIE.Platform%3DAndroid&hl=en