With Facebook, you'll want to use https://landingpage.com/ as the ad URL but then add our additional data to the "optional URL params" box.
When you generate a link in the funnel builder you can get the direct URL like so:
The full URL may look like this:
https://google.com?f=0NEijfZTGYU4&n=1MR6Bby8hvVq&ts=0WVd2QE8RwJ0&place={{placement}}&ad_id={{ad.id}}&adset_id={{adset.id}}&source3={{site_source_name}}&camp={{campaign.id}}
However, we want to split it into the base page URL and a suffix -- a similar approach applies on Google Ads, Microsoft Ads, and some other sources.
So, for your ad URL you can use the base page URL, e.g.
https://google.com
And the in the optional URL parameters box, put:
f=0NEijfZTGYU4&n=1MR6Bby8hvVq&ts=0WVd2QE8RwJ0&place={{placement}}&ad_id={{ad.id}}&adset_id={{adset.id}}&source3={{site_source_name}}&camp={{campaign.id}}
This way when the user arrives the funnel, node and traffic source IDs (f, n, ts) will be present and the Javascript will use these; and the additional data like campaign, ad set, ad ID from Facebook will also be passed.
FBCLID is automatically appended too and the Facebook config inside FunnelFlux will mean it captures this under the "external" parameter.