Issues with cross domain SSO

Hi all,

Just wondering if I'm doing something wrong or if there are issues with cross domain logins in certain environments? After logging into my primary site (domain1.com) and navigating to domain2.com/somepage, I'm getting a blank page with the following URL:

`/admin-ajax.php?action=mercator-sso-login&host=xxx.xxx.xxx&back=https%3A%2F%2Fxxx.xxx.xxx%2F&site=3&nonce=caa098e851&fragment=
`

And when I navigate to domain2.com/wp-admin, I'm not getting any mercator references in the URL at all. Just the standard login screen at:

`/wp-login.php?redirect_to=https%3A%2F%2Fxxx.xxx.xxx%2Fwp-admin%2F&reauth=1`

I've tried a bunch of things but can't seem to get it working. sunrise is defined in wp-config.php and judging from the first url, mercator seems to be loading fine. I'm not using the mercator-sso plugin since it now seems to be included in the core mercator repo and I get n "already defined" error when trying to use both.

I'm running php 7.3 and nginx 1.16. Any insights would be great!

Cheers