Hi @Zhorzh_Spasov ,
I acknowledge your concern. That said, keep in mind two important things: 1) the product you are referring to no longer exists; meaning you can't use it and the lifetime license is no longer valid. 2) the company was acquired by Microsoft and no longer exists.
While it's a poor analogy, it is equivalent to me reaching out to Alphabet about my photos in Google Plus, the product and entity no longer exist, so those help desk tickets go into the "2018 acquisition can't answer" bucket.
Here's what I would do: turn this conversation into a positive one for your client. Give them the facts, they will appreciate you stepping up and informing them, absolutely 100%, explain why "lifetime" licenses really don't exist and use this as a lesson learned and move on with Power Automate.
Please mark this answer as a solution to help others find it too. If you need additional help, feel free to msg me.