Hi @peter, thanks for your quick reply.
The REQUEST_BODY I posted may have given a wrong impression. I mainly posted it regarding content. As I said, to avoid formatting issues I followed the tutorial I linked, and used the same shell commands.
How to write a custom client interfacing a Mender server
There, shell variables are (re)-used for the process. I am in particular wondering what may be the issue if I am following the tutorial exactly. The process is still up to date, right?
Thanks for the fake mender client link, I will check it out. And thanks for your help.