As per the subject, I have a site with a Mikrotik router and I want to create a VPN connection to it for a client. The Mikrotik is a secondary router and sits behind the client's ISP router and I have all the necessary ports forwarded to it (500, 1701 & 4500).
I can connect to it from another Mikrotik router and from Android, but I have now tried multiple Windows machines and none of them want to connect. It eventually times out and tells me I have to check the network settings. On one of my tests I connected my local Mikrotik router to it and forgot to disconnect, then tried to connect my Windows machine's VPN and it actually worked. This obviously means that by going through the existing tunnel I bypassed whatever was causing my issue, but I still don't know what this issue is and why neither Mikrotik nor Android is bothered by it