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This is by design that the app insights sdk silently no-ops when given an invalid instrumentation key. One of the ways, to ensure that the configuration is correct, is to view "Live Metrics" which has a delay of 1 seconds after configuring the application. If you see data coming in for the requests made to the application, it will mean that the key is correct.
I will also reach out to the team and update this thread if I get additional information on this topic. Please let me know if you have any questions.
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