The term seems to mean the process by which a booking is made. So for example, the process of giving dates, preferences, etc. in order to book a plane ticket or hotel room, say. Example in German: "Mit der optimierten Buchungsstrecke auf Ihrem Smartphone oder Tablet können Sie ganz bequem Ihren Flug von unterwegs buchen" (Lufthansa)

The most intuitive term for me, as a non-specialist English speaker, would be booking process, but I've noticed some places use the term 'booking flow' as well - personally, I think it might be a tad literal or overly technical.

In the phrase you've given, it could be something like "If you've ever dealt with the integration of web analysis tools, then you know how complicated it can be...to integrate E-commerce tracking into a booking process/booking flow."

Booking process:
A prominent online booking button allows committed travelers to request a reservation and initiate the booking process.
https://www.homeaway.com/info/owner-toolkit/online-booking

The online booking process is at the core of all our BookingLive systems.
https://www.bookinglive.com/blog/bookinglives-online-booking...

Booking flow:

Our booking flow journey begins at the same place as a customer wishing to book a ticket: the landing page’s film selection.
http://smart-pricer.com/cinema-booking-flow/

"Online Chat: Available in the booking flow on Lufthansa.com (English only)"
http://www.lufthansa.com/hk/en/support