the column in the table do not match an existing primary key

I've got two tables tbl_Workshop and tbl_Material

tbl_Workshop has columns workshopID, workshopTitle, materialID

tbl_Material has materialID, name, workshopTitle

when I'm trying to create a relationship between the workshopTitle of tbl1 and tbl2, it gives me an error that says the column in the table do not match an existing primary key.

What could be the reason for this error and how to overcome it.

ps. The datatypes and names of both the table's column match.