Try:
set service dhcp-server global-parameters "option tftp-server code 150 = ip-address;"
set service dhcp-server shared-network-name VoIP subnet 192.168.0.0/24 "option tftp-server 192.168.0.253;"
Try:
set service dhcp-server global-parameters "option tftp-server code 150 = ip-address;"
set service dhcp-server shared-network-name VoIP subnet 192.168.0.0/24 "option tftp-server 192.168.0.253;"