There is always the possibility that there is a temporary issue on the chosen payment platform (App Store, Google, Samsung) - usually that means that you receive an error message and are unable to complete the purchase.
In any case, please make sure to contact our support or the support of the payment platform with a screenshot of the error message you are receiving.
A quick solution is always to purchase directly on our website via 
Log in there with the email address you are using in the app and Premium will then automatically also show in the app.
If you are not able to process a purchase there, please check:

- if your card is eligible for online purchases
- if your card is eligible for purchases abroad

If you still have any problem, please reach out to support via this link or through the app: Support Link