I SEE FORBIDDEN TRIANGLE IN CHECKOUT. PLEASE HELP

When I click on proceed to checkout button I see A TRIANGLE WARNING SIGN ( FORBIDDEN ) and also when I click on complete order button  it just keep loading but it never goes to the next page. 

My website: www.seyara.co.uk

PLEASE HELP.

https://forum.shopware.com/discussion/57409/forbidden-triangle-while-checkout#latest

One thread is more than enough, everything else is considered as Spam and will be deleted.