Why do I get an HTTP Error 500 (Internal Server Error) on Passback?
An HTTP Error 500 (Internal Server Error) indicates that there is a problem inside of your script or with your servers configuration. This error is most likely caused by a typo in the code or an invalid or illegal use of a function within the script. For the pass back to function correctly, then your script must be correctly set up.
HTTP errors are not generated specifically by 2Checkout. They are a part of the HTTP protocol and are common amongst all web servers. It is therefore beyond the realm of 2Checkout’s support to provide you with specific instructions for making these changes as every server is set up differently and 2Checkout does not provide server administration services as part of our support plan.
For assistance with debugging your scripts, we suggest that you contact your server’s administrator, webmaster, or hosting provider’s technical support staff.
We have observed that this error is experienced in certain web browsers more than in others, in particular within Internet Explorer. If your return page or script does not output at least 530 characters, this can potentially cause a MIME header error. Mozilla based browsers such as Firefox seem to be able to handle these pages and will display either the real error or the small output when Internet Explorer has problems. Because is an issue with the browser software itself, there is little 2Checkout can do to control this. If you are receiving this error, please try to increase the output that your return page generates to more than 530 characters or try a different web browser to see if you observe different results. Note that this is not a solution for all HTTP 500 error messages, but it is meant to be a useful step in debugging your script and has been reported as a successful step by some of our other users.