I have a 502 error on some pages of my site, I do not understand why some pages work but others display this error:

Request Method:POST Status Code:502 Bad Gateway Referrer Policy:no-referrer-when-downgrade

Problem

You have the Referer Policy set to "no-referer-when-downgrade" in Nginx, which means referer information (as your form URL) is not sent in case of downgrade (httpS submitting to simple http). And your code behind doesn't like not having this piece of information.

Solutions

1. Best is to pass everything to https :)

2. Change in your nginx.conf, the policy to:

    add_header 'Referrer-Policy' 'same-origin';
   

3. If 2. doesn't work, please do as said in 1., or you can also (but please don't do that, it's very unsecure):

    add_header 'Referrer-Policy' 'unsafe-url';
   

More: Mozilla's reference documentation about Referer Policy.

Note: origin will only set the base URL with no URI like https://domain-name.com/. While same-origin will set the full Secure URL as the Referer if it's from the same domain. It's secure since the header is passed on the :433 secure port listening.