Cannot schedule downlink using curl or MQTT

Dear Arjan

Thank you for your answer. I revised good and tried all approaches that were described in indicated pages of the forum.

I formed the link considering Using curl or Postman for the HTTP Integration on Windows
More details :

device : plug1-mcf88
application : plug1_mcf88
http integration: plug1

C:\mos>curl.exe -i -v -X POST -data "{ "dev_id ": "plug1-mcf88 ", "payload_raw ": "AQE= "}" https://integrations.thethingsnetwork.org/ttn-eu/api/v2/down/plug1_mcf88/plug1?key=ttn-account-v2.....secret key>

but i tried with and without spaces, all different combinations of *
"{ "dev_id": "plug1-mcf88", "payload_raw": "AQE="}"
"{ "dev_id":"plug1-mcf88", "payload_raw":"AQE="}"
etc. throught the curl and Postmant

But in all i have HTTP/1.1 400 Bad Request.

What it can be?

Thank you for your help