How to delete a lookup field (FieldLookup) in a list using csom

Hi there,

I'm trying to delete a lookup field in a list using CSOM but it appears not to be possible.

Tryed the following combinations:

FieldLookup columnToDeleteLU = (FieldLookup)columnToDelete;
columnToDeleteLU.DeleteObject();
list.Update();
ctx.ExecuteQueryandRetry();

OR

Field columnToDeleteLU = list.Fields.FirstOrDefault(x => x.Id == columnDelete)
columnToDelete.DeleteObject();
list.Update();
ctx.ExecuteQueryandRetry();

And I always get the error:

I tried to use the

 var primaryFieldID = columnToDeleteLU.PrimaryFieldId;
list.Fields.FirstOrDefault(x => x.Id == columnDelete).DeleteObject();
list.Update();
ctx.ExecuteQueryandRetry();