Your domain forum.simplestudios.dev
redirects me to the FreeFlarum website, that means that the problem is on your side, as my friend had this problem too for the first time setting it up. Unfortunately I don't know how he solved it and I'm pretty sure he won't remember it now, because he is busy doing things. Sorry :/
Edit: From the screenshot, it is quite clear to me that your CNAME points to freeflarum.com
instead of tetretalk123.freeflarum.com
. But as Sanguine said, you should send us your domain setup for better assistance 🙂.