[could not establish secure channel for ssl/tls with authority]

Hi There, 

I've just installed the enterprise server. 

I have installed the certificate for pulseway.mydomain.co.uk 

I've also added the CA to trusted roots.

however in the server admin config - I'm getting this error when attempting to set the web server:

I'm not too sure which FQDN I am supposed to enter here - I've tried pulseway.mydomain.co.uk and also the full PC Hostname FQDN?

The certificate works from outside the network, and I can land on the web app sign in page without any cert error - however, the same error shows when trying to login:

any help would be very much appreciated as I'm lost as what else to try!

Thanks!