You're seeing just the callback fetch_ticket, go back to WeChat.Storage.Client module for more information.
Link to this callback

fetch_ticket(appid, type, args)

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fetch_ticket(appid :: String.t(), type :: String.t(), args :: term()) ::
     expires_in: term(),
     timestamp: term(),
     type: term(),
     value: term()
  | {:error,
       __exception__: term(),
       errcode: term(),
       http_status: term(),
       message: term(),
       reason: term()

Fetch ticket of WeChat common application, the option of type parameter is "wx_card" or "jsapi"(refer WeChat Official document).