RafaP I see you are using the endpoint https://api.cognitive.microsoft.com which is for bing resources which were created under cognitive services namespace i.e most likely before October 2020. Try using the API under bing https://api.bing.microsoft.com if you have recently created your resource.
Your request should look like something below:
curl -H "Ocp-Apim-Subscription-Key: <yourkeygoeshere>" "https://api.bing.microsoft.com/v7.0/news/trendingtopics?mkt=en-US"
I hope this helps!!
Update: Editing the endpoint params, did not edit the custom config params from the initial OP post while posting the answer.