I am happy, you found it useful.
I am able to change the quantity and value automatically gets calculated.
However if in your case it is not calculating, then there could be following reasons:
- Slow internet, every time you change quantity application automatically picks the Tax rates from product database and hence take some milliseconds to recompute all amounts. After changing quantity of rate, wait for a second, you should see orange loading bar.
Other than this there should not be any issue. As I am able to do it correctly.
Can you please comment the procedure to arrive at error you got? I will try same thing and check whether I also get error following steps you followed.