“TestComplete PKCE Handler – Failed to verify the login request”

This is a Community Forum, you need to open a Support Ticket via https://support.smartbear.com/testcomplete/ 

For license issues as rraghvani suggested contact support. However, providing additional information would be of help.

What type of license do you have https://support.smartbear.com/testcomplete/docs/licensing/about.html, what version of TestComplete you are running, and are you running in a VM or desktop?

If you are using ID-Based follow the requirements in https://support.smartbear.com/testcomplete/docs/licensing/id-based/activate.html 

If you are using Key-based follow https://support.smartbear.com/testcomplete/docs/licensing/key-based/troubleshooting/index.html 

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I am also seeing this error once I tried to use the 15.8 update.  I have machines using 15.78 that work.

If anyone figures out how to resolve please post so everyone doesn't have to wait for support.