How to pass CID between two domains?

[#1]

Hi all - I would like to know how to pass CID between two sites to track conversions. Here's the scenario.

I have Google Ads running and my URLs have CIDs attached to them. 

When a person clicks the ad and goes to landing page one, they then click another button to go to another landing page with a different domain where they fill out a form. 

Is there a way to carry the CID over from landing page 1 to landing page 2?

[#2]

So your user journey is:

click Google Ads ad --> open landing page on 1st domain --> click a link --> open landing page on 2nd domain --> fill up form --> submit form (conversion)

I assume that you're tracking the 2nd domain to the same report suite as the 1st domain.

Are you already using cross-domain tracking to pass your visitor ID over from the 1st domain to the 2nd domain? If you are, then AA should be able to link the user journey properly between the 2 domains such that you don't need to pass the CID over as well.