I found the solution to the problem below by adding Apples single sign on to my windy-account than logged out on iOS and logged back in the premium account which I paid on Google Play Store was also active on my iPad. If this doesn‘t help you might find the solution by clicking on the following link:
Hi there, I use an iPad and an Android-Phone. I am a premium windy user on android. Is it possible to get the benefits of premium also on my iPad without having to pay double the premium fee? The App „Park4Night“ does this, it works there, so technically it is possible. Please Windy: Implement „pay once for all platforms“. Thanks!