As WP Travel is a complete booking package for trips and tours with its own payment gateways. Payment issues can be faced by the client during the booking process. So please once go through the full article, you will find all the possible reasons and solutions for solving this problem.
Sometimes the payment issue may be raised due to the incorrect payment key added in the backend. So, make sure that you have added the correct payment keys.
The payment you have integrated may not support the currency that you have selected. For example, WP Travel PayU Checkout payment gateway doesn’t support Dollar Currency but you need to select the Poland currency as Poland Zloty (zł) for the payment procedure to work.
For details on currency support view the compare table.
Third-party plugin conflict:
Third-party plugin conflict can also be one of the leading causes of the error in the payment system on your site. So, please once verify the issue by deactivating all the third-party plugins and activating only the WP Travel plugins.
For the conflict check, please follow the link.
Test Mode/Live Mode:
Adding the live key to the test mode and adding the test key to the live mode may also cause an issue in the payment.
Live mode: If you want to proceed with payment in Live Mode then disable the test mode by going to Admin Panel > WP Travel > Settings > Debug as shown in the screenshot. Also, make sure you added the live key.
Test mode: If you want to proceed with payment in Test Mode then enable the test mode by going to Admin Panel > WP Travel > Settings > Debug as shown in the screenshot. Also, make sure you added the test key.
Standard PayPal Payment:
If you are using the Standard PayPal payment gateway, then you have to set IPN.
For detail regarding setting IPN, please refer to the given link.