If I get what I think you are trying to achieve, I don't think it is possible with just a printer.
1) You'll need some hardware to act as a webserver that can turn the HTTP requests into something the printer understands. Printers don't really have webservers built in to them with HTTP APIs.
2) Firewalls will be a problem even if you have a dedicated webserver. Most likely you'll add some hardware that connects to a central service as a client, and your central service will relay messages down to your device on site.
1) You'll need some hardware to act as a webserver that can turn the HTTP requests into something the printer understands. Printers don't really have webservers built in to them with HTTP APIs.
2) Firewalls will be a problem even if you have a dedicated webserver. Most likely you'll add some hardware that connects to a central service as a client, and your central service will relay messages down to your device on site.