The simplest and safest option is to contact the hosting provider. HTTP/2 is included free with most modern plans, while HTTP/3 may be enabled in the hosting or CDN control panel.

Message for support

Hello,
HTTPS is already working for example.com.
Please confirm that HTTP/2 is enabled for the canonical website address.
If the infrastructure supports HTTP/3 (QUIC), please enable it as well
while retaining HTTP/2 for compatibility.
After the change, please confirm which protocols are externally available.

When the website uses Cloudflare or another CDN

  1. Confirm that DNS traffic is actually proxied through the CDN rather than using DNS-only mode.
  2. Find HTTP/2 and HTTP/3/QUIC support in the network settings. Labels and locations can change.
  3. Keep HTTP/2 enabled. Enable HTTP/3 as an additional option when the plan supports it.
  4. After the change, purge CDN cache only if necessary and verify the protocol from an external connection.

Technical notes

  1. Back up the web-server configuration.
  2. Identify where HTTPS terminates: Nginx, Apache, a proxy, load balancer or CDN. The protocol must be enabled at that layer.
  3. For HTTP/2, verify TLS support and ALPN negotiation with the h2 value.
  4. HTTP/3 requires QUIC, UDP port 443 and support from the server or CDN. Do not disable HTTP/2.
  5. Use the server's normal configuration test before a restart or reload.
  6. Test externally and confirm that pages, APIs and assets still load correctly.

Exact directives depend on the Nginx or Apache version, control panel and proxy layout. Do not paste an arbitrary configuration without checking the documentation for the installed version.