it looks like you have sent your local login address to your salesperson. One thing should bear in mind that
The salesperson should be on the SAME network as your computer to assure she can access that local link
If it is confirmed, one more thing is that your computer have to be ALWAYS turn on the Express Invoice programme in order for them to be able to access.
If she works remotely (from home, other branch, etc.) over the Internet to access your computer, it means you need to tick the highlighted box in the image below.
Hope it helps.
Cheers
Henry