Heatmaps not working

Hello, our client uses connect matomo successfully for tracking basic analytics for their wp-sites. However, they would like to use heatmaps as well. Our on-prem matomo has heatmaps plugin installed and it is working correctly with non wp-sites. When this customer tries to query our on-prem Matomo (from the wp-server) they get an cors error. The same cors error appears for the basic tracking request (data is still saved to on-prem matomo). We have added their domain to CORS-domains in Matomo. How to get heatmaps to work with connect-matomo? The customer also has a login on their page. Is that a blocker issue for using heatmaps on wp-site?