I see you mention you’ve tried several requests/urls so maybe your example might be just a mixture of them all, but, I wanted to make sure that the URL you are using for blink has …/v1/blink and not …/v5/blink on it:
I also wanted to ask you if your device is in y local network and if you have tried those requests from an application container (SSH-ing into it)
you can do as follows (requieres balena-cli):
sudo balena scan
balena ssh
(inside the device):
curl -X POST --header "Content-Type:application/json" \ "$BALENA_SUPERVISOR_ADDRESS/v1/blink?apikey=$BALENA_SUPERVISOR_API_KEY"
This can help you check that the supervisor is up and running property and try to isolate the problem either to the supervisor or the api configuration
I hope it helps, please come back to us if you need further help
as I can see the base URL that you try is api.balena-cloud.com which indicates that this is a balenaCloud connected device.
For debugging, can you please share the output of this request (obfuscated as you need):