Hi Pradeep,
There is no "one-size-fi)ts-all" solution for this. Your solution is unique to how your site is setup. For example, does your form have a unique URL the visitor has to go to? Or is it some button you click and you get an overlay on a page? Is it embedded as an iframe on your site?
However, below are the two common methods to trigger a counter event in adobe analytics for form submissions
Method: To trigger a counter event when a submit button is click
<button onclick="myFunction()">Click me</button>
<script>
function myFunction()
{
s.events="eventN”; // eventN is the event assigned for tracking the number of form submissions
s.tl();
}
</script>
Note: This is just a sample custom code,however it will change based on the website
Here, s.tl(), function is mandatory to trigger a counter event in adobe analytics, Since you are facing a trouble in tracking, please check whether a s.tl() is added in the custom code
Refer to this link to understand the importance of s.tl function:
https://docs.adobe.com/content/help/en/analytics/implementation/vars/functions/tl-method.html
Method 2: If the "thank you" page has a unique URL, can the user only get to it upon successful completion or similarly if there is a attribute like “submitted successfully, thank you for submitting the form” in a unique element Id as a part of dom, you can trigger a counter event to track the successful form submissions in adobe analytics.
Hope this helps