Hopefully Telegram is paying Sunfirecasino.com a commission since a Telegram account is required for support. I will not be opening a Telegram account, thus I will not be receiving any support.
I just recently visit their website just for the sake of checking whether your statement is true.
Live support on the casino website is available on the bottom left corner with message icon. Most of the casino have their own telegram channel that you can seek support too but they always have the standard live support on website in contrary to what you claim.
Maybe he's comfortable to used telegram that's why he suggest those things, but I guess he should deal with their support on where they are recommend to contact them. Since going on that platform might put him on risk since there's lots of impersonation happening and he might got an issue with this then get scam by imposters.
So better he should deal with them thru online chat support since provably that aside from they are safe from scammers they can get in touch with their real support.
The issue maybe the response time but this is still ideal venue for him to raise his concerns or issues.