The setting is on lines 273-277 of confirm.php. You have:
$WA_PP_ECO_Set_params[0][$nextIndex] = "ReturnURL";
$WA_PP_ECO_Set_params[1][$nextIndex] = "https://www.sportsmedicalcertificates.com/pp_confirm.php";
$nextIndex = count($WA_PP_ECO_Set_params[0]);
$WA_PP_ECO_Set_params[0][$nextIndex] = "CancelURL";
$WA_PP_ECO_Set_params[1][$nextIndex] = "https://www.sportsmedicalcertificates.com/checkout_failure.php?ppcancel=1";
You don't have to go back to the office.... I updated your .htaccess file for you using the FTP information you provided. I updated it to:
RewriteEngine On
RewriteCond %{HTTPS} off [OR]
RewriteCond %{HTTP_HOST} !^www\. [NC]
RewriteCond %{HTTP_HOST} ^(.*)$ [NC]
RewriteRule (.*) https://www.%1/$1 [R=301,L]
This will ensure that everyone that visits your site will see the https:// version and will use www. in front of the domain. That matches the return url setting in your confirm.php page so that should fix the issue.
