Curl produces different results when invoked via systemd vs command line

Question

I have the following unit file:

[Unit]
Description=Sends a message to a discord channel

[Service]
Type=oneshot
ExecStart=curl --header "Content-Type: application/json" --request POST --data '{"content":"MESSAGE TEXT HERE"}' https://discord.com/api/webhooks/WEBHOOK_ID_HERE/WEBHOOK_TOKEN_HERE
DynamicUser=yes

# No [Install] since this is meant to be used with a timer

Running the curl command that is in ExecStart manually posts the message to the Discord channel that corresponds to this webhook, while starting the service produces the response {"code": 50109, "message": "The request body contains invalid JSON."} from the Discord server.

Is there any notable difference between running a command through systemd and directly? For example, I could not find any indication that there might be a maximum command length for ExecStart.

Answer 1

Solved. Thanks to A.B's comment I realized I had \ns in the message, and as it turns out systemd interprets them before executing the command. Escaping the slashes (\\n) solved this and now it works.