I think you should not use the service url but the item to find this.

For example:

https://www.arcgis.com/sharing/rest/content/items/c1a3bf98b1d148a6917ad85662d82704?f=pjson

This will return a json with “sourceUrl”.

Also see https://developers.arcgis.com/rest/users-groups-and-items/item/

You can also use the REST api endpoint under AGOL. To get to the services directory, on the item page you will find URL in the bottom right corner

https://support.esri.com/en-us/knowledge-base/how-to-access-the-rest-and-admin-endpoints-of-an-arcgis-000027990

The at the bottom of the endpoint you have alot of options from there to explore