Bing sent out a final reminder this morning that today is the last day you can use version 11 of the Bing Ads API. You need to migrate to version 12 if you want to still use the Bing Ads API, version 11 will not work tomorrow.
Bing posted this notice on Twitter:

A final reminder to API clients. All clients must migrate to version 12 by October 31, or you will no longer be able to use the #BingAds API. For more information, look here:
— Bing Ads (@BingAds) October 30, 2018
Bing wrote, “With the release of Bing Ads API version 12 in April, we announced the sunset of API version v11 will happen on October 31, 2018. If you are currently using API v11, which is now deprecated, this is a courtesy reminder for you to migrate to API v12 by the sunset date.”
Here is how to migrate to version 12 of Bing Ads API.
Forum discussion at Twitter.