REST API does not support UTF-8

We just tried to use the REST API to support the missed events feature, but stumbled into the problem, that all the messages delivered now via REST API are incorrectly encoded in some way.

Example: In the Build Started message we have:

gerrit review <CHANGE>,<PATCHSET> --message '⚫️ Build Started <BUILDURL> <STARTED_STATS>' --verified <VERIFIED> --code-review <CODE_REVIEW>

However, when this message is posted to gerrit, it appears as:

?? Build Started https://.....

When I post the message myself using postman, the bullet appears correctly. So it seems to me that the REST Request is not encoding correctly or explicitly uses latin1 or some other charset that doesn't support this glyph.