PayPal issue with persistent checkout_failure page

Greetings WebAssist team, I have a thorny issue that has perplexed me for the last day. I am in the final stages of a website redevelopment project and have hit a wall with the PayPal checkout option. I had some issues that I had solved with the incremental price feature I coded following your excellent tutorials. My local checkout is working fine now but when I click the PayPal button the checkout page the modal window pops up and only shows the checkout_faillure.php page. I have checked the code over and over again and cannot see why the PayPal option keeps failing. I have created an FTP username and password that can use to access my development server. To recreate the problem go to:

https://www.bugbitingplants.com/Dev/sundrews.php
Add any in stock sundew plant to the cart from the details page
On the checkout page click the PayPal button and you will see the error. Any help you can provide will be greatly appreciated and result in my being able to finish this project.

Regards,
Robert Crespo