CHAP Secret gone when reboot

I set up pptp server on openwrt on OpenWrt 22.03.0-rc5 r19523-bfd070e7fa installed on VPS. It was all working fine, but all username and password set on chap-secret file, gone when I rebooted the server. I don't know or maybe it was only the chap-secret because OpenVPN works fine when reboot.

Where did you save the username and password? What was the file path you used?

Meanwhile, pptp is not secure and is considered unsuitable for the modern internet. You should remove this vpn protocol and use something that is robust and secure such as wireguard?

Where did you save the username and password? What was the file path you used?

on /etc/ppp/chap-secrets but that file was a link to /var/etc/chap-secrets. Even though I deleted them and create a new file, it will always back to default.

Meanwhile, pptp is not secure and is considered unsuitable for the modern internet. You should remove this vpn protocol and use something that is robust and secure such as wireguard?

SSTP Server is not supported (yet?) on OpenWrt so I opting to use PPTP. Wireguard on the other hand, was implemented on Mikrotik Router OS V7 but it has a bug on hotspot setup. I only use VPN to remote client side which behind NAT firewall

this file should not be erased on reboot...
what is the output of df -h

this one will be erased on reboot because it is in RAM only... but it is generated at either boot time or at PPTP interface bring-up (I forget which) from the file in /etc/ppp.

If the PPTP packets are traversing the internet and the PPTP port is open on an internet facing host, you are at serious risk using this protocol. It is trivially easy to crack and will be a target from botnets all around the world.