On MT300N-V2, you missed open port, the firewall configuration as below:

config redirect                                   
		option target 'DNAT'   
		option src 'wan'       
		option dest 'lan'      
		option proto 'tcp udp'    
		option dest_port '80' 
		option name 'wan_lan'     
		option dest_ip '172.16.0.1'
		option src_dport '80'

config rule 
		option name 'Allow-web'
		option dest_port '80'
		option proto 'tcp udp'
		option src 'wan'
		option target 'ACCEPT'

config redirect                                   
		option target 'DNAT'   
		option src 'VPN_client'       
		option dest 'lan'      
		option proto 'tcp udp'    
		option dest_port '80' 
		option name 'vpn_lan'     
		option dest_ip '172.16.0.1'
		option src_dport '80'

Besides, the 80 port should be opened on your LAN device.