It says the secret was already opened
We cannot recover it, and that is the feature rather than a limitation.
Why support cannot help
We never had the content. It was encrypted in the sender's browser, and the key travelled in the link, not through us. Once the view was used, the ciphertext was deleted.
What to do
Ask the sender to send a new one. If you did not open it yourself, tell them: someone with the link did.
Still stuck? Contact support, or send a secret of your own.