302 is a redirection, I don't thing thingSpeak would provide that to you directly. A wild guess is that your network is redirecting the request away from ThingSpeak. Are you able to update the channel from a browser or GET using POSTMAN connected on the same network? You can use the syntax below, which is shown here in the documentation.
https://api.thingspeak.com/update?api_key=<your Write API KEY>&field1=1010
Are you able to update the channel this way?