That page is just an iFrame to JotForm, so any PHP code on that page is not affecting how the form is submitted, since the form is not on that website. I don’t know how JotForm works, but you have to control submissions, and how things are submitted though JotForm.
The JotForm have some options to incorporate the form, Javascript Link, iFrame, and PopUp with <a> tag in html.
May these others options can work? Or i have to see with their support?
Right now, it looks like you have the form to redirect to mostrar.php once it is submitted, and that PHP file is trying to read POST or GET data, correct?
You have to tell the form that it needs to send POST or GET data when it redirects to mostrar.php, and there may or may not be a setting for that in JotForm settings.
They have the cited method option ’ Send Post Data ', i change to Yes but nothing changed. I saw that my problem is not with the site but with Jotform. Tks for support and explain <3