When I wanted to create new links it said that I have to upgrade to premium (My 6-month premium package have just expired), but when I wanted to buy the same package again it said “Validation Error”. And now I want to change my billing info but I don’t know where?
You can update your billing info on the Upgrade Account page (Login - LingQ). Just choose Membership Plan you want and click on “Upgrade Now” button. You will then be able to choose from 1,6 or 12 month membership, and you will be able to edit your billing informations bellow.
Let me know if you have any additional questions.