The browser generated HTTP ERROR 500 page is generated 99.99% of the time by your PHP code crashing.
There are all kinds of reasons why it could crash. It might be an error in the code, a compatibility issue with our hosting or just a configuration issue that needs to be addressed before your code will work here.
Which of those is the case for you? Just follow the instructions in this KB article:
This should produce a usable error message which is the first step to resolving that error. If you need help making sense of the message, you can share it here so we can help. But we do need that error message to help you.