Ahhh why you don't accept customers from Germany? Am so sad, I wanted to try your website out so bad!

Try speaking to their customer care on their site and ask them if VPN usage is allowed in your case. That could help!
Yes, that's right, as usual, sometimes there are users who are reckless in trying to use a VPN just to test the site and gamble there when they are prohibited from playing because they are on the list of countries prohibited by the site, there is no other way than to ask service support because that is important so that problems do not occur. In the future, we often find cases like that on this forum just because of problems using VPN and from countries where the site is prohibited.
I don't know if Germany is banned by Roobet or maybe it is if you want to need an explanation and the reason why they banned it the most important thing is to visit the site then use VPN ask their support service is it safe to use VPN and why Germany is banned from accessing the site, if indeed the support service Having said that there are no problems using a VPN, it will definitely be safe for gambling.
They should avoid using VPN since its prohibited by majority of casino so they should never try to use it without asking their support so that no issue on their account will happen.
Also we can see here which country allow or disallow Roobet to operate
https://silentbet.com/roobet/where-is-it-allowed/I don't know if there's changes happened but as we can see base on the article Germany is not listed on restricted country so he should be fine accessing it. But if he can't access the site then its really better for him to contact Roobet support so that he can get a clear answer regarding to this situation.