Tracking via GTM

We have setup Piwik PRO code using GTM.
The code is installed on a subdomain, howvere all the pages in Piwik PRO show the main domain so instead of https://xyz.domain.com/url they show https://www.domain.com/pageurl

The base code in GTM is loaded via custom html
and page is tracking using piwik pro template

How do we fix this issue?

You can close this. It was user error.