I'm trying to add a constraint to my excel file, but every time I add the binary constraint, I get this error ""binary constraint cell reference must include only variable cells"
It looks like it's almost undocumented.

I figured it out. In order for binary constraint to work, you have to use cell reference of cells used in the Set Objective cell. If you try to set the binary constraint to cells not mentioned in the Set Objective cell, then this error will always occur.