How to connect electron with custom SIM to the Internet, without connecting to the Particle cloud?

When I try this with a photon I call:

SYSTEM_MODE(SEMI_AUTOMATIC);

and in setup() I call

WiFi.connect();

What is the alternative of WiFi.connect() for the electron?
I tried without it, and the electron just blinks white.

I have

SYSTEM_MODE(SEMI_AUTOMATIC);
STARTUP(cellular_credentials_set("internet.proximus.be", "", "", NULL));

https://docs.particle.io/reference/firmware/electron/#connect-

thanks