How to connect two SharePoint on-premises installations inside the same domain using JSOM?

I have two SharePoint installations in the same domain.

Example:

Installation 1: subdomain.domain.com/sites/mySite

Installation 2: subdomain2.domain.com/sites/mySite2

Also, they share the users. I would like to read a list from Installation 1 in a Installation 2 web part.

I tried using JSOM with new SP.Context(siteUrl) and SP.RequestExecutor.js, but I got this error message:

Access to subdomain.domain.com/sites/mySite XMLHttpRequest at from origin has been blocked by CORS policy