How to add an entry to a Matrix PP:
def pp = api.findLookupTable("MarginBySegment")
def entry = [:]
entry.lookupTableId = pp.id
entry.key1 = segment.Mfr
entry.key2 = segment.PBG
entry.key3 = segment.PBU
entry.key4 = segment.PRC
entry.key5 = segment.ProductDesignEligible
entry.attribute1 = pvs.low
entry.attribute2 = pvs.target
entry.attribute3 = pvs.high
api.addOrUpdate("MLTV5", entry)
Key was to have the lookupTableId in the values map.
Alternatively, one can skip the findLookupTable call and specify the PP name directly in the values map:
def entry = [:]
entry.lookupTableName = "MarginBySegment"
entry.key1 = segment.Mfr
...
api.addOrUpdate("MLTV5", entry)