Why doesn't tracking_data SOMETIMES come to the webhook?

Question

API

Hello viber chat bot developers.
I am developing a chat bot on viber.
Sometimes I encounter a problem that tracking_data webhook does not fit.
For example, 2 logs in a row:
there is

{"event":"message","timestamp":1557594511506,"chat_hostname":"SN-CHAT-16_","message_token":5308045791643970853,"sender":{"id":"nsszrJAOly5pSc7MKBSqBQ==","name":"\u0415\u0432\u0433\u0435\u043D\u0438\u0439 \u0413\u0430\u043B\u043A\u0438\u043D","avatar":"https://media-direct.cdn.viber.com/download_photo?dlid=jaX_40zWJ5o4GhFJAGF7vGaYkmcb6zZl2qUnrZJReeYL7sTJiHlh7AGFJckB0xmVg83PkmoK3QIOjIr9gAVKAv33m9KKkddlE1HDS2RALRWrV3nviE836fvPJB0&fltp=jpg&imsz=0000","language":"ru","country":"UA","api_version":7},"message":{"text":"offers","type":"text","tracking_data":"{\"referred_by\":\"\",\"phone_num\":\"[phone]\",\"user_id\":\"143\",\"card_num\":\"00241\",\"barcode\":\"9900000002411\",\"verified_email\":\"1\",\"currrent_action\":null,\"job_id\":null}"},"silent":false}

but not in the next log.

{"event":"message","timestamp":1557594767112,"chat_hostname":"SN-CHAT-02_","message_token":5308046863787727631,"sender":{"id":"nsszrJAOly5pSc7MKBSqBQ==","name":"\u0415\u0432\u0433\u0435\u043D\u0438\u0439 \u0413\u0430\u043B\u043A\u0438\u043D","avatar":"https://media-direct.cdn.viber.com/download_photo?dlid=jaX_40zWJ5o4GhFJAGF7vGaYkmcb6zZl2qUnrZJReeYL7sTJiHlh7AGFJckB0xmVg83PkmoK3QIOjIr9gAVKAv33m9KKkddlE1HDS2RALRWrV3nviE836fvPJB0&fltp=jpg&imsz=0000","language":"ru","country":"UA","api_version":7},"message":{"text":"my_discount_menu","type":"text"},"silent":false}

Under what circumstances may tracking_data not be transmitted?
With what it can be connected? Who faced?
Testing on phone and PC.

Answer 1

This is a parameter that allows you to track forwarded messages, as far as I understand
Allow the account to track messages and user's replies. Sent tracking_data value will be passed back with user's
reply