The subject of carrying luggage on a Xootr Swift has been discussed before but this is my latest solution.

The Arkel quick release rack and bag are ideal for folders that need to keep the seat post clear for the fold to operate. The rack attaches via a Q/R bracket to the saddle rails and a rubber collar clips around the seat post and is secured by a Velcro type strap. There is no pressure on the seat post so you can use the rack with carbon posts. The bag attaches to the rack using four Velcro straps. The bag and the rack can be removed in a few seconds so will not interfere with the bike's fold.

The photo shows the rack on my Swift with the (supplied) extender arms in place to lower the rack further down the seat post. Once set up you can fit and remove the rack and bag in no time.