There are two methods to retrieve the invitation ID. The first one can be done directly in the user panel by going to the "Collect" section in which you will the "Send via e-mail" option.
Then, select "Enter manually". If you already have respondents added, skip this step.
After adding the respondent, select the “Configure mailing" option, which is at the bottom of the screen.
In this step, choose any option that will allow you to proceed to the next step:
Choose the invitation template of your interest.
After selecting the template in the browser bar, id_template will be added to the URL, which you can use further.
As mentioned before, there is another method of retrieving the invitation template ID by creating an appropriate Webhook. You can find more about this method in the link below: