Custom URL Parameter for Published to web reports

Hi, recently I was tasked to make a report that can be filtered by company id and such. Earlier, I used a secure embed feature on Power BI to embed the report to my website. I used the URL filter parameter to pass the company id, and it works. But after switching to public report (published to web), I can't use the URL filter anymore. Obviously, this is because publish to the web doesn't support filtering on the access URL. But then, I found this report made by Politico ;

|https://app.powerbi.com/view?r=eyJrIjoiZTA5N2VkYWQtYmNiMS00YWFmLWEwZWQtOGY4MmExNTlmZjllIiwidCI6ImMyOGQyZTEyLTA5ODgtNGFjZi1iZGJhLTExOTU4MmU4ZDA4ZCIsImMiOjl9&Country=Belgium

, where they can change the "Country" parameter in the URL to change the displayed data of the country, like France, Germany, or Poland. For me, this is basically a filter, but I still didn't know what the parameter is doing and how. Does anyone have any idea how they did this? I've tried filters, drill through (even though it's obviously not), even report parameters.