Amplitude newbie here so hoping to learn from someone who has done this before. We're trying to implement cross-(sub)domain tracking between our marketing site (think example.com) and web app (think portal.example.com). Right now we have Amplitude on both sites but the user histories are not stitched together, as if Amplitude can’t merge the IDs.
We are following the steps in the documentation https://help.amplitude.com/hc/en-us/articles/115003135607#h_f717e48c-460c-4a17-abd7-102327673798 but on step 2 we cannot use URL parameters because of the nature of the experience, only third party cookies would be viable. How can we implement a third party cookie that sends the device ID to the portal site so that, even if time passes between user visits the marketing sites and then converts, we can track it? Has anybody found a best practice to accomplish for subdomains in particular?
Thanks in advance!
PS: reached out to support already but they don’t have any example implementation beyond the URL parameters solution which is here: https://developers.amplitude.com/docs/advanced-settings