PPPoE authentication issue with older ISPs

Hi Guys, I had an issue authenticating my OpenWRT (21.02 on Asus RT-AC56U) with older ISP that still uses PPPoE. Obviously there was no problem with credentials and the same router would connect on stock or Padavan! After 3!!! weeks and countless attempts of finding solution here or on the internet there was no luck!(( But the solution was very simple, so I decided to share with those unfortunate of you, who may have faced the same issue and may be close to giving up))...

In /etc/config/network add this line to your PPPoE interface options:

option pppd_options 'refuse-eap'

Also, in my case connection is more stable when WAN interface is disabled.