Hi @kaviyaayyappan,
I’m sorry about the confusion here, we recently changed the way snippets are executed to provide more precise reports for when fatal errors are being thrown but in this case it looks like you should be able to find the issue by searching for “username” in the list of snippets (top-right search) in the admin.
If you already know which snippet is causing the issue simply search for “username” in the code and you should be able to find that it is being used as an array key without a check that it is actually set. You will likely find something that looks similar to: $array['username'] and you will have to add a check if username is set.
Please reach out using the form at if you want to share the code privately and we can provide more guidance there.