1. The redirect URL doesn't support the "Transaction Status" field because redirection from the checkout page only happens after a successful transaction. In case of a transaction failure, an error is returned which is displayed on the hosted page.
If you're looking to track failed signups, you can use the Abandoned Cart Report in Chargebee.
2. You could pass the unique Identified as the customer/subscription ID to the checkout page and this will be returned in the webhook response. You could also configure the redirect URL to receive this value.
If you're using the plan specific hosted pages, you can pass the subscription ID value in the below format
And here's the format of the redirect URL to retrieve the subscription ID
Hope this helps.