Facebook API marketing: issues with creating custom audience

问题

I try to add users by APPUID to custom audience. I do post to the url https://graph.facebook.com/v2.10/CUSTOM_AUDIENCE_ID/users with this payload:

{ 
  "schema": ["APPUID"],
  "app_ids": ["<APP_ID>"], 
  "data": [["<ID1>"], ["<ID2>"], ...]
}

Data contains 5000 APPUIDs. The response is:

{
    "invalid_entry_samples": {},
    "audience_id": "<AUDIENCE_ID>",
    "num_invalid_entries": 0,
    "session_id": "<SESSION_ID>",
    "num_received": 5000
}

But after that the delivery status for this custom audience is: "Audiences must include at least 20 people to be used for ads.".

What am I doing wrong? And why is the size of the custom audience smaller than 20?

来源：https://stackoverflow.com/questions/47071822/facebook-api-marketing-issues-with-creating-custom-audience