Dimension Mismatch Error during dot product in Python
Firstly user_vecs, item_vecs are matrices, not vectors, since both the shapes are of two dimensions. If seems like you are trying to multiply both the matrices, so you can simply use user_vecs.dot(item_vecs). No need to transpose item_vecs. You can also use np.matmul(user_vecs, item_vecs).  Refer to this thread for more details.