Using Parameters from RequestURL in URL

[bristermitten]

I have an nginx server setup to serve images from a certain directory, with an endpoint at img.url.tld
On the backend, I have NextCloud setup which I am able to upload images to via ShareNix using this configuration

{
      "Name": "nextcloud",
      "RequestType": "PUT",
      "RequestURL": "https://nextcloud-instance.tld/remote.php/webdav/img/$Y$-$M$-$D$_$h$-$m$-$s$_$n$$extension$>",
      "Username": "<>",
      "Password": "<>",
      "ResponseType": "Text",
      "URL": "https://img.url.tld/"
    }

This will obviously create a file like img/2021-07-01_22-50-01_931438699.png, but I can't figure out a way of getting the 2021-07-01_22-50-01_931438699.png part to then use in my URL field, as of course, only regex / json / xml parameters can be used

Is there a way of doing this, or do I need to make a fork / setup another script?

Thanks