How do I use Airport Express In-town Check-in without paying the train fare twice?

What this answer depends on

• Hong Kong and Kowloon Airport Express In-town Check-in; supported payment credentials and participating operating airlines only
• In-town service is not a universal substitute for airport check-in. MTR lists participating airlines and station-specific arrangements, with codeshare exclusions where another airline operates the flight. Confirm the actual operator and current service at the intended station before traveling there.
• The practical payment step is using the same supported credential at both entry points. Switching from one card or device credential to another can prevent the system from treating the entries as the same journey; use the exact MTR instruction rather than assuming two credentials linked to one bank account are interchangeable. The latter is a precaution, not a claim about a particular wallet’s token system.
• MTR describes smart check-in kiosks that retrieve the trip from a travel document or boarding pass and support seat confirmation. Entering the service area is not itself airline check-in. Follow the kiosk result and use staff assistance when the document cannot be read.
• MTR collects the Airport Express fare at In-town Check-in entry and instructs users to use the same supported credential at platform entry without a second collection.
• In-town Check-in depends on station and participating operating airline, with codeshare conditions.
• MTR describes smart kiosk trip retrieval and seat/check-in steps, with assistance when travel documents cannot be read.