Scenario
Created a matrix item and the item is available in the Webstore but the Matrix option is not available for selecting
Solution
Navigate to Customization > List, Records & Fields > Transaction Item options.
(Transaction item options are fields that you can ass to the line items of your transaction records to gather information specific to your business needs. Item options can refer to the characteristics of an item. For Example, You can record multiple colors of an item as item options.
Select the item option corresponding to your matrix item. Verify whether the “Webstore” checkbox is marked under the “Applied To” sub-tab. If the checkbox is unchecked, the item option will not appear on the web store for selection.