Coinbase Pro data download not working

The problem with Coinbase Pro is that there is no way how to get the first available date of the specific symbol.

At least it is not documented https://docs.pro.coinbase.com/#get-historic-rates

API example 

If no start parameter is provided then API returns data only for few last hours/days based on the granularity (timeframe). 

This is a reason why you need to enter correct start date manually and cannot use Update selected, Update all.

So if anybody have some idea how to get the first available date, please let me know :)