I am a freelance website editor currently working on a site, it desperately needed it’s PhP updating. After doing so, I had text errors at the top of my screen due to the widgets that come with the theme. The current theme is called Industrial and I cannot update it without generating a token. However, I was not the one who purchased the theme, it was someone else, and nor myself or my client have access to whatever login details were there to get the theme activated.
If you do not have access to the account which purchased the license, then you unfortunately have to buy it again if you want to update the theme. Ideally, your client should buy it with his account so he won’t face the same issue in the future when you eventually won’t be working with him anymore.
You should notify the theme owner about it on theme sales page or PM.