i am trying to merge multiple polygons of a feature. i select them via select features by polygon and use the advanced digitalizing toolbar " merge selected features" option. it worked for some but mostly i get: error occurred during merging operation.
I find that it sometimes gets confused if there are too many nodes on shared lines between features. Chack the geometry validity of the features too because geometry errors can cause problems. Also you could try adding features one by one and not trying to merge all of them together at the same time, if it isnt too time consuming
Merge tool will merge other polygon to selected polygon. So if want to merge all other polygon to single polygon then select and merge.