Parameters not working

I tried to create a test shortcode with parameters as described at
https://help.xyzscripts.com/docs/xyz-wp-insert-code-snippet-premium/faq/how-can-i-pass-parameter-using-the-snippet/
but I can’t get it to work. This is the test snippet I wrote:

`echo “This is a test snippet”;
//$category={category};
//echo “<br>category= $category”;
echo “<br> category= {category}”;

Running it just produces
This is a test snippet
category= {category}

And, if I uncomment the lines prefixed by // in the test snippet. The program crashes with a critical error due to the { in line 2.