You can share custom audiences between ad accounts when both accounts are linked to a business portfolio and have an audience-sharing connection. If you want to share custom audiences, you need to meet the requirements such as both parties must have a business portfolio. The person with full control of the business portfolio must initiate the sharing process and accept Facebook's terms of service the first time you share. To share an audience, go to Audiences in Ads Manager and click the box next to the audience you want to share. Next, click the Share button and enter the ID of the ad account you want to share the audience with. Finally, click the Share button again.