WP Refused to display 'URL' in a frame because it set 'X-Frame-Options' to 'sameorigin'

I'm a beginner to WP development, I'm editing a plugin to add third-party payment gateway when i did the same code in normal php files i didn't had any error and it worked yet in WP cURL didn't follow redirect so i sent it to the front end to show it in IFrame and it works fine and shows the one time password and after sending it it give me the error and says the third-party refused to connect, i tried editing .htaccess file but it didn't effect. can you guys help me with this or how to make cURL follow redirect (cURL is enabled from the server)
the html string response

!DOCTYPE html
html
head
    title/title
/head
body onload=OnLoadEvent();
    form name=downloadForm
          action=url
          method=POST
        input type=hidden
        !-- To support javascript unaware/disabled browsers --
        noscript
            center
                Please click the submit button below.br
                input type=submit name=submit value=Submit
            /center
        /noscript
    /form

    script language=Javascript

                    !--
                    function OnLoadEvent() {
                        document.downloadForm.submit();
                    }
                    //--
    /script
/body
/html