Hi. I have a license of avast premium for 1 device. I want to add another one. Couldn’t understand how to do it. For the meanwhile I cant even install the free version, no clue why 
Please help…
Not sure why you can’t install Avast Free on another system, it shouldn’t have anything to do with your existing license.
Submit a support ticket https://support.avast.com/en-ww/contact/sales in your case select the Billing, payment, or license issues option - and then the I have a different billing or license issue and click Next and follow.