Need help on a new setup for openVPN on windows server for Android clients - VPN isn't working
Android won't work with tap. Use tun. See the wiki.
Your other option may be recompiling the kernel in Android so it'll support tap.
Another important consideration is that tun is more efficient. The tap (virtual Ethernet) mode must be only used when absolutely necessary. Don't use it unless you know for sure you need it and can explain why.