If you have something like

badlop — Wed, 28 Mar 2018 11:14:37 +0000

If you have something like this:

    listen:
      -
        port: 5281
        ip: "127.0.0.1"
        module: ejabberd_http
        web_admin: true
        http_bind: true

then add the starttls and certfile options, like this:

    listen:
      -
        port: 5281
        ip: "127.0.0.1"
        module: ejabberd_http
        web_admin: true
        http_bind: true
        tls: true
        certfile: "/etc/ejabberd/server.pem"

See https://docs.ejabberd.im/admin/configuration/#examples

ejabberd - Comments for "How to configure HTTPS in ejabberd 17.09"

If you have something like