To add an entry to a Matrix Pricing Parameter:

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)

It is important here to have the lookupTableId in the values map.

Alternatively, you 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)

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