A Unity ID allows you to buy and/or subscribe to Unity products and services, shop in the Asset Store and participate in the Unity community.
Separate names with a comma.
Andy from PlayFab summarizes it nicely in his response here :...
I can confirm that this is still an issue for anybody trying to restore purchases on iOS when using PlayFab with Unity IAP 4.1.3. Still receiving...
Still irritating in 2020.3.21f1