The Open Geospatial Consortium (OGC) API links shown on the Open Data site (via the API dropdown) concatenates the service type for Web Map Services (/MapServer/) and also removes the service name and type for Web Feature Services (/Test/MapServer/).
Browse to the source of the service from the dataset page (at the full service level rather than the indexed layer level). Click the WMS or WFS link, and copy the URL from the browser to be used.