How a thank you page works
When someone submits an enquiry form, the site has to tell them it worked. The tidiest way is to send them to a separate URL that exists only for people who have completed the action. Because nobody arrives there by accident, a view of that URL is a reliable signal that the form was actually submitted, which is why it is the most common trigger for a conversion tag.
The alternative is an inline message that appears without changing the page. That is fine for the visitor but harder to measure, because there is no new URL to count. In that case the tracking has to listen for an event the form fires instead, usually through Google Tag Manager. Both approaches work; the mistake is assuming one is in place when the site is doing the other.
Why the thank you page matters
Two jobs sit on this page at once. The first is measurement: if the page is where your conversion is counted, then every reporting figure, every bid strategy and every judgement about which keyword pays comes from it. Break the page and the platform loses its ability to optimise, because it no longer knows which clicks turned into enquiries.
The second job is the enquiry itself. A person who has just given you their number is more willing to act than they will be at any other moment, and a page that only says thank you wastes that moment. Telling them what happens next, and by when, reduces the chance they contact three competitors while waiting to hear from you.
Where thank you pages go wrong
The most damaging fault is a page that can be reached without converting. If it sits in the menu, is linked from a sitemap, or is bookmarked and reloaded, the conversion count inflates and your reported cost per lead looks better than it is. It should be excluded from internal links and, in most cases, from search indexing.
Redirects cause a quieter version of the same problem. If the form sends the visitor somewhere else before the tag fires, or the page reloads on a slow mobile connection and the visitor leaves first, conversions go missing. And where a business runs several forms, sharing one thank you page across all of them makes every enquiry look identical in reporting, so a newsletter sign-up counts the same as a quotation request.
How to get it right
Give each meaningful form its own confirmation URL, keep those URLs out of the navigation, and check the tag fires by submitting a real test enquiry and watching it appear. Then read the page as a customer would: say what was received, who will respond, and roughly when. Add a next step that suits people who are still curious — a relevant guide, a phone number, or a WhatsApp link if that is how your customers prefer to talk.
If the counting itself is the shaky part, fix that before anything else. Reliable conversion tracking is what turns a thank you page from a courtesy into a measurement point you can bid on.