Input error: k: Format of site key was invalid

I created a form following this topic about free trial registration

https://s2member.com/kb-article/how-can-i-offer-a-fixed-term-free-registration/#toc-4bc5fa96

I did everything that it says, like changing site example.com with mysite.com and set the level to 1 instead 0 as suggested.

When I pasted the code here’s the message where it was supposed to be the text link to the popup stripe form

Security Code.
Input error: k: Format of site key was invalid

Why is that?

https://www.ads-software.com/plugins/s2member/