Critical Error Can’t get on Site

So our client reached out to us saying that their website is down. I just have a login and no other information about their site on https://www.peteralleninn.com/wp-admin but as you can see all it tells me is:

There has been a critical error on your website. Please check your site admin email inbox for instructions.

I do not have an admin email inbox that I am aware of. How do I fix this? Is there any way to contact www.ads-software.com support?

The page I need help with: [log in to see the link]