When using the backtracks parameter, there is a hard limit set to 20 per one call.

But you can combine it with a backtrack parameter to go further back in history with additional calls.

The backtrack sets the candle from which you then request the 20 backtracks. It sound a bit complicated, but it works quite easily.

Here's how I'd query 60 historical values split into 3 different calls:

All you need to do is to just set the backtrack parameter to 20 more with each call, that will set the starting point of your query that many candles back.