Force the FCM connection via a proxy?

[Duy Johnny Khac Nguyen]

I am developing an electron app with react. Everything works fine except that the FCM connection doesnt connect via my clients proxy. So their network denies any furhter connection to the m.talk.google connecitons.

He says that the connection needs to connect via a specific port on their proxy.

I am quite new to Electron, so not sure how to solve this. Any ideas? Any way to configure the FCM connection to go via some port ?