get
https://sandboxapi.legendtrading.com/v2/app/countries
查询国家列表 (Retrieve Country List)
返回所有国家的列表。若返回值的 prohibited 字段为 true，则表示禁止该国家用户注册。
Retrieve a list of all countries. If the prohibited field in the response is true, user registration from that country is restricted.