Post the introduction if you’re unable to establish initial connect, then kindly report the issue on your dashboard. Ensure you've tried every means to reach out to the party after fetching the contact details available on your dashboard.
However, if the initial connect has already been established and the party is now not responding, then it would simply mean that they may not be interested to pursue the transaction with you. You may follow up after a few weeks if you wish to and then move on and explore the possiblility of connecting with other parties on the platform.