Check your subscription key
Make sure that you are using the correct subscription key for your new price tier. You can find your subscription key in the Azure portal. To check your Azure Bing Search subscription key, go to the Azure portal and navigate to your Bing Search resource. Click on the Keys and Endpoint blade, and your subscription key will be displayed in the Primary key field.
If you just changed your price tier, it may take some time for the new quota to be applied to your account. Try waiting a few hours or overnight, and then try again.