It's possible that it may take some time for your subscription upgrade to take effect on the Bing Search API. Your subscription type and service determine the number of quotas per second (QPS) you can make, so it's crucial to ensure that your application stays within your quota. If the QPS limit is exceeded, requests will fail and an HTTP 429 status code is returned. The response includes the Retry-After header, indicating how long you need to wait before sending another request.
However, the exact amount of time it takes for your subscription upgrade to take effect may vary. It's recommended to wait at least a few hours up to a few days after the upgrade before attempting to use the API again and see if the issue persists. If the problem persists after several days, then you may want to contact Bing Search API support for more information.
I hope this helps!