Difficulty Including payment.php File Content in checkout.php on Live Website

Description:
I’m encountering an issue with my website where the content of the payment.php file is not being included in the checkout.php page, specifically on the live website. This problem occurs even when the user is logged in. However, on my local development environment, everything works as expected.

Steps Taken:

Verified file paths to ensure correctness.
Checked file permissions for payment.php to ensure it’s accessible by the web server.
Implemented error logging to check for any PHP errors or warnings during the inclusion process.
Attempted to debug the issue locally, but couldn’t replicate it.
Ensured server configurations (PHP version, settings) on the live website match the local environment.
Cleared any caching mechanisms to rule out caching-related issues.
Question:
What could be causing this discrepancy between my local environment and the live website? Are there any server-side configurations or permissions I should check specifically for including PHP files? Is there a recommended approach for troubleshooting such issues in a live server environment?