No trusted relationship error when sending a push notification

Hi guys

We are receiving the following message when attempting to send a push notification:
The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.

Any idea how we could fix this? When logging into our environment via the OutSystemsNow app we receive the following message: "The certificate for this server is invalid. You might be connecting to a server that is pretending ... "

It then asks whether we would like to continue. When we indicate that we would like to we are allowed to log in.

Any help or suggestions would be appreciated.

Thank you