I installed the purchasing package. Latest 4.5.0 version and also the verified version 4.1.5.
The problem is that there is no unity purchasing folder in plugins. Also there is no “import” button as the guides suggests.
Can’t find it any where.
Yes, the Asset/Plugin version of IAP is now replaced with Package Manager. There is no need for Import, sorry for the confusion. Our documentation needs updating. You might want to look at the Sample IAP Project v4 as a complete example project with IAP https://discussions.unity.com/t/700293/6 and https://docs.unity3d.com/Packages/com.unity.purchasing@4.5/manual/UnityIAPGoogleConfiguration.html
Thank you!
While searching for solution I thought I was alone with this problem. Now I understand that everyone got it right with this example 
And update the documentation will probably save others some time as well