Your account may be pending for one of two reasons:
If you're an established customer who has previously run ads and now have your account in pending status, then you need to add a payment method. Once you add a payment method, your account will become active.
If you're a new Bing Ads customer, your account will remain in pending status until you've completed the following setup items:
You'll be up and running within 10 minutes of completing setup. If not, please contact Bing Ads Support for further assistance.