GCLID

Without it stored on the lead record, offline conversion import is impossible. You can know a deal closed, know which form produced it, and still have no way to tell Google — because the thing that connects the deal to the click was thrown away when the visitor clicked to the second page.

It is also the failure with the worst timing. Nobody discovers a missing click id until they try to feed outcomes back, which is months after the leads arrived, and the fix does not apply retroactively.

• Read it on landing, write it to a first-party cookie with a sensible lifetime, and populate a hidden field at form render.
• Store it on the CRM record, not only on the form submission, so it survives the handoff into sales tooling.
• Watch the expiry window. Google’s import has a limit on how old a click can be — long cycles need the value uploaded at an interim milestone rather than at close.
• Capture the siblings too. A funnel that only handles GCLID silently loses its iOS traffic.

Exactly the same bug described under hidden fields, and it is worth stating twice because this is where it costs money. Reading the click id from the URL at submission time works perfectly in testing, where you land on the form and submit immediately.

It fails in production for every visitor who behaves like a considered buyer — landing, reading, navigating, returning, submitting. The click id is captured for the impulsive and lost for the deliberate, which biases everything you subsequently feed back to the platform.