First, I stitched (right sides together) the flap to the exterior back side, not the part with the twist lock button, like it is explained in step 12 on p.99.
Then, I inserted the exterior bag, (right side out), with flap and small strap loops down, into the lining bag (wrong side out). The pocket of the lining should be at the side of your bag where the flap is attached.
Now , with the 1 cm seam allowance, the earlier 5 mm seam is covered.
I turned the bag right side out through the hole in the lining and topstitched the bag top edge.
You get this:
Do you see the shoulder strap loops? They are strongly fixed between exterior and lining.
Then, following step 15 and my tutorial, I applied the eyelets.
This was the scary bit; with one wrong scissor movement I could destroy the bag.
I clipped on the shoulder strap and handle and ... finished!
I enjoyed making this bag.