What is the relation between SLEEP_RQ pin and sleep mode AT code, do I need both to enter sleep mode?

What is the relation between SLEEP_RQ pin and sleep mode AT code, do I need both to enter sleep mode?

Yes, you need to first enable sleep mode on the endpoint using the command:
 
ATSM1
 
and then pull the SLEEP_RQ pin high to enter sleep. Pull the pin low to exit sleep mode.