I already suspected it was some cache/cookies related problem, so I made the suggestion, since your Edge browser could access it and the others couldn't
I try to claim free spin many times on Duelbits during Christmas and Easter event with VPN without any problem. The support suggest it too since the provider of the free spin doesn’t allow me to play as long as I will just use that provider for claiming the free spin. I also have a default VPN on since I have premium subscription. VPN is only risky if you will use free VPN since they are using shared IP that might connect you to other user. Worst to user that violates the casino ToS.
In the specific case of the user who was having problems I didn't recommend it, because trying several browsers, and then several different IPs using the VPN could do more harm than good in his case, since we didn't know the cause.
But I agree, it's not good to use free VPNs due to this issue of shared IPs
I believe that the shared IP was the issue.
You just can't participate in the promotions anymore, or you can't place bets either?