>> The only think, my fellow colleagues told me is, that the CN=SapDev is incorrect, because it is not pingable from the Internet.
Your colleages may be correct here.
Well, I am not sure if your saprouter SapDev has to be pingable from the internet, but it has to be reachable.
In any case it will need a public IP address, so that sapserv2 will be able to contact it.
So please check this with your network admin!
regards