Proof of content's ownership.
"If you have your story posted elsewhere, be aware we'll require proof of content ownership. You can already submit a support ticket with it to speed up the process. Accepted proofs include editing your existing description on the site you've posted your story on the earliest, or an official document marking you as the author. We may also accept an email from a known email address of the copyright holder (i.e. published on the official website or in print in the book) as valid proof of ownership."
English isn't my first language, so I might be getting something wrong, but I don't quite understand how should I file the support ticket, and I couldn't find another similar topic in this site. I already have it posted on wattpad and AO3, so I'm afraid it will be rejected if I don't fill it. Sorry if this isn't the place for questions like this. Any help would be appreciate it.
If you need to communicate with the site administrators you can easily ping the mods in the Discord chat and get a response quite easily if needed.
For proof you can just add a link to your original fictions and post some annoucnement or something on those sites to prove that you there is you here.