prevent re-submit in page reload

Hello , im trying to create a small plugin of booking ( custom post type : booking) and in my form when success submit it post it show the booking details to user, but if user reload the page it submit again 🙁

please how to resolve that that is my code of submit ( only header) :

`if ( ‘POST’ == $_SERVER[‘REQUEST_METHOD’] && ! empty( $_POST[‘action’] ) && $_POST[‘action’] == “new_post” ) {

// Do some minor form validation to make sure there is content
if(!empty($_POST[‘start’]) || !empty($_POST[‘end’])){ submit post and send email ) }}

then if success : show booking details

Else show error and the form

i tried to unset($_POST[‘start’]) and $_POST[‘end’] to prevent resubmit if success but not working,

i have one idea but i really dont know how to do it , its to get the post type just submitted in one other page by user ( not logged).

Thank you in advance if you have any idea to help me

Regards