Xan H. okay - yeah this usually happens when the web host is blocking our crawler - which appears to be the case here.
It looks to also be trying to import quite a few pages but the website looks to maybe have 6-10 pages max. The import tool likely trying to import products, which would take longer to remove from the sitemap than it would be to just generate a sitemap based on a description of the website. I would just start with a fresh new sitemap if it were me.
Apologies for the inconvenience here.