Hi @Athi Narayanan Jeyaraj The API call you are trying to use is meant for use in ARM template deployments alone. If you are trying hit the API with a PUT call, it will likely fail.
There is another API in the data plane which lets you create a Key-Value under feature flag. Try the following API end point
PUT {endpoint}/kv/{key}?api-version=2023-11-01
For the key, you can pass a value similar to this .appconfig.featureflag%2Ftest
Refer the documentation of the API endpoint Put Key Value for additional details.
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