Asking for IP-address

does it have any way else to asking for ip-address?

I have use this /sbin/udhcpc -R -b -i wlan0
and get this

Mar 24 15:26:48 swi-mdm9x28-wp user.info Legato:  INFO | NAD[872] | === ASK FOR IP ADDRESS === 
Mar 24 15:26:48 swi-mdm9x28-wp user.err Legato: =ERR= | NAD[872] | udhcpc: started, v1.27.2
Mar 24 15:26:48 swi-mdm9x28-wp user.err Legato: =ERR= | NAD[872] | udhcpc: sending discover

it was =ERR= while asking and make my program stop.
does anyone can guess me other way to asking for ip-address?

Dear customer,
In order to troubleshoot the problem, please help provide answer of the following items:

  1. Which Sierra deivce are you using?
  2. Which FW version are you using?
  3. Which wifi expander card is attached to the Sierra device?

Thanks