Hello @EddyZ !

Dear @PavelS and @OneEagle already told the good thoughts about your task (thnx, guys!). But I would interested to know your goals certainly:

1) Do you want my-second-domain.com to automatically redirect to my-first-domain.com?" (A 301 Moved Permanently redirect is recommended for SEO.)

2) Or do you want both domains to show identical content, but keep the URL in the address bar the one the user initially visited?" (Please note that this approach creates duplicate content, which is generally harmful for SEO as it can dilute ranking signals and confuse search engines.)