I have a list of 10 items with individual prices in a constant sum question and I want to set-up a custom validation so that if someone picks items that total more than 1500 an error message informs them they have exceed the maximum allowed and to choose items that total 1500 or less. I tried the 'custom validation' option and entered '<1501' but that doesn't work. Any suggestions would be much appreciated.

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One of the solution would be to use JS to calculate the total based on selected items. The calculation should be done on click of JS fake Next button and next button should be clicked programatically if total is less than 1500

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