Create a downlink from a webhook

Hello everybody,
I am having issues to send the post with the downlink information from my server to ttn, i have already create the application with two end devices that work properly, but now i want to be able to send information form my server to the end-devices via downlink. I have try to follow the format, but the information in the manual is for V2, and I need for V3, anyway i think i am very close, but i have just some issues with the authorization. I use postman to test it sending a message like that: CapturaPostman1
And a body: {

"dev_id": "eui-70b3d57ed0043164", // The device ID

"port": 2, // LoRaWAN FPort

"confirmed": true, // Whether the downlink should be confirmed by the device

"payload_raw": "0x01" // Base64 encoded payload: [0x01, 0x02, 0x03, 0x04]

And I obtain this error:
I also have the Api Key of the whole application, but i am not sure of which one do i have to use, and the where in the message (header or body) and with which key.
Thanks for the help, probably is a sily stuff