set up the captive portal on openwrt - openwrt

Question

I'm trying to set up the captive portal on openwrt.
I did all the work. And when users connect to the router, they are automatically redirected to the index.html page.
But when the Internet is disconnected, a "internet my not be available" message appears. And Android devices can not detect the captive portal page.
file /etc/config/dhcp
root#OpenWrt:/etc/config# cat dhcp
config dnsmasq
option domainneeded '1'
option boguspriv '1'
option localise_queries '1'
option rebind_protection '1'
option rebind_localhost '1'
option local '/lan/'
option domain 'lan'
option expandhosts '1'
option authoritative '1'
option readethers '1'
option leasefile '/tmp/dhcp.leases'
option resolvfile '/tmp/resolv.conf.auto'
option logqueries '1'
config dhcp 'lan'
option interface 'lan'
option start '100'
option limit '150'
option leasetime '12h'
option dhcpv6 'server'
option ra 'server'
option ra_management '1'
config dhcp 'wan'
option interface 'wan'
option ignore '1'
config odhcpd 'odhcpd'
option maindhcp '0'
option leasefile '/tmp/hosts/odhcpd'
option leasetrigger '/usr/sbin/odhcpd-update'
config domain
option name 'connectivitycheck.gstatic.com'
option ip '192.168.1.1'
config domain
option name 'apple.com'
option ip '192.168.1.1'
config domain
option name 'captive.apple.com'
option ip '192.168.1.1'
config domain
option name 'detectportal.firefox.com'
option ip '192.168.1.1'
config domain
option name 'gstatic.com'
option ip '192.168.1.1'
config domain
option name 'clients3.google.com'
option ip '192.168.1.1'
config domain
option name 'connectivitycheck.android.com'
option ip '192.168.1.1'
config domain
option name 'msftconnecttest.com'
option ip '192.168.1.1'
config domain
option name 'play.googleapis.com'
option ip '192.168.1.1'
config domain
option name 'spectrum.s3.amazonaws.com'
option ip '192.168.1.1'
config domain
option name 'mtalk.google.com'
option ip '192.168.1.1'
config domain
option name 'alt3-mtalk.google.com'
option ip '192.168.1.1'
config domain
option name 'alt4-mtalk.google.com'
option ip '192.168.1.1'
config domain
option name 'connectivity-check.ubuntu.com'
option ip '192.168.1.1'
I think that android devices send packet ICMP for check internet.
I using iptables drop all ICMP packet. But it did not work again.
Note
This problem occurs only when Android users connect. Ubuntu and Firefox recognize the index page.