How to get the parameters on page and avoid 404?

Hi all,

I have this page https://localhost/mypage

and I want to set some $_GET parameter like that:

https://localhost/mypage/firstparameter/firstvalue

I need “firstparameter” value but I always end in the 404 page.

I’ve spent some hours with get_query_var(), add_query_vars_filter() and add_rewrite_rule() but no way…

Thank you