Warning: A non-numeric value encountered – Error-message inside booking

We have an unsolvable problem: on our new website locationtours.ch the plugin called “Bus Ticket Booking with Seat Reservation” unfortunately displays an error message instead of the price during the checkout process. The error message, which unfortunately is also displayed in the frontend instead of the price, is:

Warning: A non-numeric value encountered in /home/clients/edc4307184857ac0555c07528a201047/sites/locationtours.ch/wp-content/plugins/bus-ticket-booking-with-seat-reservation/inc/WBTM_Woocommerce.php on line 719

This is also the reason why we’ve currently put the website into maintenance mode. We suspect that you might need access data from us to reproduce the error. If so, please let us know. However, I want to provide you with all system-relevant information in the form of screenshots.

Unfortunately, your website https://mage-people.com/support-desk/ is not working correctly.

We believe the error is not related to our website, as our system is generally up to date and does not display any errors. Therefore, we ask you to check your plugin and, if necessary, provide an update so that we can get the website up and running as quickly as possible. Thank you very much!

We can’t send the Support Desk form to you because, unfortunately, an error message keeps appearing. Please contact us by email so we can resolve the issue.

We also find it strange that you don’t provide an easy way to contact us on your website https://mage-people.com (no email address, etc.) and that all of your links to your social media channels are broken. This is unprofessional!

The page I need help with: [log in to see the link]