How to get multi selected table records in VBCS from Button action chain

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We are on JET 9 and implemented multi select table with checkbox. Its displays data fine. But when we select the rows using checkbox, we would like to retrieve those rows from Button (like Submit) Action event chain, construct json and call OIC integration.  Most of the examples shown are from selection listener of table where it displays data based on selection event.

I see selected attribute in table data, but dont know how to map a variable to it as it expects keyset type. any pointer will be helpful

How to get the selected table rows from button action chain ? any example or reference would be helpful.