Typo3 - Formhandler HTTPS-Problems

i'm using Typo3 6.2.25 and i can't use my Formhandler on Production Server with HTTPS. Everytime i try to send a contact-request i get :

Mixed Content: The page at 'https://www.example.com/' was loaded over HTTPS, but requested an insecure XMLHttpRequest endpoint 'http://www.example.com/index.php?&id=1&L=0&randomID=xxx&field=&uploadedFileName=&eID=formhandler-ajaxsubmit&uid=xxx'. This request has been blocked; the content must be served over HTTPS.

ich changed my .htaccess Rewrite Rules to:

RewriteRule ^(.*)$ https://www.example.com/$1 [R=301,L]

and now i get:

Failed to load https://example.com/index.php?&id=1&L=0&randomID=xxx&field=&uploadedFileName=&eID=formhandler-ajaxsubmit&uid=xxx: Response for preflight is invalid (redirect)

Can somebody help me with this problem?