Knowledge is power.
As per my knowledge if you have a hosted account, then you cannot earn through AdSense from sister sites. Please check your main AdSense account if it is mentioned in the top right-hand corner as a "hosted account". The new policy was implemented by Google some years back. Please refer - https://adsense.googleblog.com/2012/11/updates-to-application-process-for-host.html.
So, in order to upgrade your account to a non-hosted one, you can set up your own site, put up good quality content on a consistent basis, and then submit that site for a review by the AdSense team. On approval, you will then get to earn from that site and from any other blog/site that you contribute at, including the sister sites of ISC. You could check out this experience and get some useful tips on upgrading to a non-hosted account.
I will inquire with Tony Sir if the information that I have provided here is correct.
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