JSOM report validation error on https://www.openstreetmap.org/way/304526745#map=17/41.914449/45.475963 : 
"type=multipolygon on a way. Should be used in a relation (1)."
Likely mistype and need to remove this key-value, but I never worked with multipolygons so not sure. If you mean something else, fix error please.