Issue with accessing custom order page

The “Book a Service” button on my website is linked to the default order page. When clients assigned to a custom order page click that on my website, they are taken to the default order page. Even after logging in, they remain on the default order page.
According to customer service, the only way to avoid this is for the client to specifically go the the URL of their custom order page (bookmarking it) and log in from there. I can’t expect all my clients with custom order pages to always remember to order through their link instead of our website. We need to make it easy for them to access their designated order page no matter where they log in from.

There should be a redirect set up so that the system redirects an agent to their custom order page after they log in.