Mandatory information about my setup:

Joomla! version: 3.3.6
PHP version: 5.4.17
MySQL version: 5.5.40
Matukio version: 5.1.3
Direct link to the page that shows the issue: https://activ-ha.com/evenements


Description of my issue:
Trying to pay an event booking with either cash or check payment plugins bring a RFI shield protection error on admin tools, thus stopping the user to pay and blocking its IP
This behavior seems a threat to the website.
Can you tell us what is going on with these plugins and matukio and help solve the problem ?
Thanks
Jean