You may have already setup a unique tracking URL parameter during your Skyscanner onboarding process which will be present on all user redirects from Skyscanner (e.g. ?utm_source=Skyscanner). You can use this parameter as a variable in the tag manager trigger conditions and use it to identify Skyscanner traffic. If you do not have this, we can configure it for you upon request.
When the UTMs are not being carried through to the confirmation page (the URL changes once the user lands on your site website), an alternative solution is needed. We suggest using a cookie or localstorage to save the referrer, or the 'dataLayer' concept in the Google Tag Manager: https://developers.google.com/tag-manager/devguide#datalayer
You can then configure the tag to fire on specific page loading conditions and/or URL parameters. If the source of traffic does not persist between pages (eg. in the form of a URL query parameter), you can write it to a cookie and use that in the trigger condition.
Please keep in mind that the conversion event should be fired when the traveller reaches the "booking confirmation page" and not before to avoid over-counting conversions.