Yes, if you want to use a Twilio SIM in an Electron you need to put it in DFU mode (blinking yellow) and execute the command:
particle keys server --host id.udp.particle.io --port 5684
The reason is that there was special support for Twilio SIMs in system firmware, but the servers that support it no longer exist. Until that code is removed, the command above will revert the behavior to be a normal 3rd-party SIM on a per-device basis.
You’ll also probably need to use a 30-second keep-alive.