One of my webservices is returning 502. It's a new webservice and it was installed part of a new plugin after upgrading the server from 3.8.3+ to 3.11.3+ (php7.4/Ubuntu/nginx1.7).
The webservice works fine in the development environment (Macbook pro MAMP 3.11.3+) and staging (Win2016 server XAMP installation). I looked in the php.log on the server but there are no errors there just bunch of unrelated NOTICE messages.
I found a similar post (https://moodle.org/mod/forum/discuss.php?d=225495), but it wasn't related to the error I'm having. I tested on Chrome, Safari, and Edge but the error was on all 3!
The service itself doesn't do anything special, it returns $data from an exporter bookings->export($renderer);