This error basically means that you tried fetching data for a given date but it doesn’t exist.
This happens because you are using an optional when data is not available on the end-date.
The possible End-Date could be a Trading holiday like (2020-01-01)
The solution to this is given in the TODOs themselves. You can combine the condition of data existing on a given date as well not existing on a given date by simply ensuring you always use data of the last date for which it is available and since the response contains data only for available dates.
For example if the data is not available for 2020-01-01, Try running it for 2020-01-02, and you will get the data.
This is an FAQ Query for QMoney.
Closing this topic as it has been solved by you yourself. Great job, keep working hard. if its not resolved feel free to un-mark the accepted solution to re-open the topic.