I have 7 shapefiles which I would like to combine using the 'Merge shapefiles' function in QGIS. I got the error message that the shapefiles must all be the same geometry. I checked this, one shapefile has the geometry 'WKB type - PolygonZ' - I think this was a shapefile created when I used the Vector-dissolve function. All the other files have the geometry 'Polygon'. How do I change the geometry of this shapefile - or is it a case of recreating and re-saving the original shapefile?
This should work without complaint in QGIS 3.0 and greater - the output layer will be a PolygonZ type, and the Polygon input features will be upgraded to PolygonZ geometries to match.