If you sold your art outside of Jack Arthur you will need to either remove it from your Jack Arthur profile or mark the work as sold on Jack Arthur.  

To update the artwork, login to your profile, then go to More > Portfolios in the navigation and click the relevant portfolio, then click the relevant artwork.  Once the artwork is displayed, click the Edit icon in the lower right corner of the artwork. Locate the Availability field and change the option to Sold.