I have emailed several days ago without any response .
I would like to know if I can use the paid SIP feed for internal calculations as well as for display on my stock scanner. Users are authenticated and pay a subscription fee to access the scanner.
@sking Alpaca data is licensed only for your personal use and does not permit commercial use of that data. You cannot provide the data, or derivations of that data, to third parties. So no, you cannot use it for a scanner that others can access.
Alpaca is working on additional licensing arrangements, which should be available in the next six months or so. Those may allow for commercial use. In the meantime you may want to check out massive.io. I believe they offer different licensing, which may work for you.