If you're experiencing errors with process payment page you have to change "Use Virtual Process Payment Page" to No and use Process Payment page (Tickera > Settings > General > Pages). Shortcode which has to be included in the page is [tc_process_payment]
If you are using Stripe, make sure that you haven't accidentally switched Secret API Key and Publishable API Key places:
In case you see this notice on Payment Page it means that you are using one of the Payment Gateway (Stripe, PayPal Pro) that requires SSL Certificate to be installed on your site. To install SSL Certificate on your site you have to contact your host company.
If this happens, there is most likely a problem with the session path on your website.
To resolve this, navigate to Tickera Settings -> General tab -> Miscellaneous area and set Create and Force new session path option to Yes (see the screenshot below).