Spark it looks like FreeFlarum correctly picked up the CNAME record, but something went wrong between your domain registar and FreeFlarum. When I removed custom domain of your forum, it worked normally which means that your domain registar is likely the culprit there.
Please check if you are using any proxies or third-party domain services. The record at Cloudflare is set up correctly, but something else might be interfering. Since I don't know the details of your setup (whois search suggests that you are using something alongside Cloudflare), I'd recommend re-checking all the settings and contacting that service's support if it doesn't work.
