admin login not working

Hi there.

I’m using pantheon for our hosting.

If I try to enter my admin dashboard using this url

https://mysite.com/wp-admin

I can not login

but if I try

https://live-mysite.pantheonsite.io/wp-admin

it works.

The thing is our client like to be able to login using

https://mysite.com/wp-admin

How can we set our wordpress to work with the two urls.

I think the problem is because of the simple ssl plugin.
Please advice, how can i add another rule redirection
to ignore the admin login page.

thanks