ThrowError / ThrowException shows up only in the bottom for few seconds.
This message should be parsed after the price or on top of the page (after the Menu Bar), stay there for user to read and if there’s more than one Error, they should be divided somehow or splitted on new lines each.
In the example image:
* User forgot to enter order data
* Error pops up on the bottom of the screen for few seconds
* User cannot read that fast, also there are several errors in one row (BAD!)
* User can’t understand what happened – leaves page, no order
