Can't enable XSIM become 1

Hello, Guys.

I had problem that if I config nRF9160 through UART0 (default) it works and I receive IP address and can make MQTT connections.

But when I use UART2 (external MCU) I can't make it work: XSIM stays 0 even if I set it to 1.

Is there is some manual which commands should be sent to make it work.

Also should I have add for external connections SLM_INDICATE and CONFIG_SLM_WAKEUP_PIN?