Google have updated their policy which now requires application to have the billing library updated to 7 or 8.
You can update your current IAP Version 4.13 or use the pre packages for IAP 5 which include this with the general release of IAP 5 coming by the end of July.
To access pre release package and get a jump on the general release you can add the package by name in the Package manager by doing the following.
- Open Package Manager
- Press the Plus button
- Add package by name
- Enter com.unity.purchasing in name
- Enter 5.0.0-pre.7 in version
You can find all the details for the changes in our change log which can be found here.