Why are my links flagged as unsafe?

I've been using Rebrandly for some time now and have never had a problem with the servie until now.

The problem is as follows:
I received an email saying that my domain isn't working. I get in, restart the DNS verification process and the status indicator turns green again.

But every browser flagged my shortlinks as unsafe( ERR_CERT_AUTHORITY_INVALID or
"The certificate chain is not complete.")

I think the problem is that in the domain details (in Rebrandly Domain Managing page), the SSL field says: "SSL Certificate is not active yet". But to my knowledge, Rebrandly would provide free SSL certificate for me, so why does my domain not have SSL Certificate?

How can I resolve this issue? Thank you all in advance!