The FCM documentation for iOS integration should come with a warning that onBackgroundMessage should not be used if the platform is iOS. This 2019 issue comment saved me from a mysterious error that was throwing an exception that did not reveal its or

Google suggests enabling gzip compression before transferring files over the network:

In order to receive a gzip-encoded response you must do two things: Set an Accept-Encoding header, and modify your user agent to contain the string gzip. Here is an example of properly formed HTTP headers for enabling gzip compression:

Acc