From: https://community.safe.com/s/question/0D54Q000080hKVxSAM/featurewriter-postgis-cannot-set-geometry-type

Answer:

"PostGIS writer doesn't have the option to specify geometry. A few earlier build might have had this parameter exposed by mistake. Since each PostGIS table is allowed to have mixed geometry types, the writer doesn't provide the parameter to restrict it to one type.

However, if you need to only write features that are postgis_multipolygon, you can use some transformers to filter the features by geometry type, before they get into the writer.

I'm not 100% sure what postgis_multipolygon type can or can't have, or what exact restrictions you want to use for your scenario. Some likely transformers to look at would be GeometryFilter and AggregateFilter.

If you can give a bit more background on why you want to restrict the writer geometry, and what is not allowed to be written, our other experts should be able to give more detailed suggestion on how to filer the features."