Hi,
As logs says, Apple is trying to stop people using HTTP in favor of HTTPS. I think they introduced it in iOS 12. Its not really related to Unity or plugin version.
So you have to either change address to use HTTPS or add an domain which you want to use as an exception in your plist file so OS will allow it to be used with HTTP. I am sure you can find how to do that.
Let me know if you need more help.