You have a faulty prebid.js implementation on page.
- Prebid codes were copied or imported but required changes were not made.
- You forgot to fill the values for ad units or used another way to fill in ad units
- Review this guide on AdUnits: http://prebid.org/dev-docs/adunit-reference.html
- See where you have implemented empty AdUnits array which could look like:
window.adUnits = ;
pbjs.adUnits = 
- Apply changes accordingly