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 completion. If not and your account remains pending thereafter, please contact Bing Ads Support for further assistance.