Hi Hoang,
In my understanding, you need to buy a new license for Skype for Business server 2019 due to Skype for Business sever using different license from
2019.
About more information about licensing for Skype for Business, you can read this article:
https://products.office.com/en-gb/skype-for-business/it-pros.
In addition, this problem is more related to licensing. Our forum has limited knowledge of this aspect. So, if you want to get more help, you can contact
Licensing Support.
Thanks for your understanding.
Best Regards,
Sharon Zhao
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