WeChat.BatchSends.batch_send_by_list

You're seeing just the function batch_send_by_list, go back to WeChat.BatchSends module for more information.
Link to this function

batch_send_by_list(client, batch_send_by_list_body)

Specs

batch_send_by_list(WeChat.client(), batch_send_by_list_body()) ::
  WeChat.response()

根据OpenID列表群发【订阅号不可用,服务号认证后可用】 - 官方文档