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Add the autogenerateKeysInPP application property (in the advanced configuration) and set its value to true.
If any MLTV (MatrixLookupTableValue, i.e., Matrix PP value) has in its metadata set that a key is read-only, it will not be possible to insert a key in the UI, and the server will autogenerate a key with a (nearly) unique value that should be parsable even to double or long (64bit-signed) type.
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