Thank you for your post and welcome to the TeamViewer Community!
The free version of TeamViewer can only be used in a purely private environment, e.g. for conencting to your friends and family.
Every use of TeamViewer in a work environment (e.g. connections to customers, colleagues, offices, schools etc.) would require a licence.
If your friend is interested in purchasing a licence, he is welcome to contact us by phone or email: https://www.teamviewer.com/en/support/contact/
We will be happy to help him choose the licence that best suits his needs.
I hope this answers your questions. If there is anything else I can help you with, please don't hesitate to let me know.
All the best,
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