There is a known issue with the link used to complete a workflow, which will result in anyone following this link receiving a _This site can’t be reached_ (or similar) error in their browser.
As an interim fix we have published and update so that all new Workflow share links will now generate with a sine.co/wf/ prefix. Please log in to your account and copy a new share link for your workflow, or update your existing link, replacing ‘si.ne’ with ‘sine.co’.