Several raspberry Pis in different networks

Hello together,

I’m new to this forum. Right now I’ve set up 5 RPis inside 5 different locations, all connected though VPN.
As long as they all on the same network say, I can acess all of them through their webinterface.
The very moment, I have only acess through the VPN network, the webinterface does not repsond anymore. To be more precise, I get an initial reaction acessing i.e. 10.0.0.x, but the website never completes in the browser.

Any thoughts?

Brgds DerBusIsVoll