By default if you create an advert or campaign in facebook ads manager (https://business.facebook.com/adsmanager/) and it's a draft, other users will not be able to see or edit the advert.
To get around this there are 2 options:
- Pause & Publish: If you need to collaborate on a campaign, set the campaign to paused then publish it. It won't run but your ads will go in for review. This is a bit of a bonus because when you activate later there will be no review delay or potential disapproval. Once published and paused the ads will be visible to other users on the account.
- Creative hub app: If you just need creative reviewed, you can do that by creating advert mockups with creative hub: https://www.facebook.com/ads/creativehub and other users with access to creative hub will be able to view and feedback on the ad creative. These ads can then be pushed from creative hub to ads manager to start running.