Despite the fact PPTP is not recommended due to security reasons, sometime it is useful due to its simplicity.
I tried to configure it and it works with my android phone (Xiaomi running Miui 9.5 which is based on Android 6.0.1) without any issue:
/ip pool add name=pool-pptp ranges=192.168.101.10-192.168.101.250
/ppp profile add dns-server=188.8.131.52 local-address=192.168.101.1 name=profile-pptp remote-address=pool-pptp use-encryption=yes
/ppp secret add name=launtel password=fastly profile=profile-pptp service=pptp
/interface pptp-server server set authentication=pap,chap,mschap1,mschap2 default-profile=profile-pptp enabled=yes
/ip firewall filter
add action=accept chain=input comment="Allow PPTP VPN" dst-port=1723 protocol=tcp
add action=accept chain=input comment="Allow PPTP VPN" protocol=gre
On my phone, I didn't set anything special - just type of VPN, username and password. Only caveat might be the encryption: With
I can either enable or disable the PPP encryption in android. With
I can use VPN only with disabled PPP encryption in android. With
I can use VPN only with enabled PPP encryption in android.
Since we don't know what setting you use, neither what does your log say, this is the best I can do. As said earlier, it would be good to have some log info. For example like this:
/system logging action add name=vpnlog target=memory
/system logging add action=vpnlog topics=pptp