Azure AD Domain Services Secure LDAP Question

I have a question regarding the setup for the internet public part. I'm thinking it was not set up correctly but wanted to ask ideas. Basics is the following
Old Domain. Example Acme.lan

We migrated our three programs to Office 365 and have 3 FQDN's in 365
Say
one.org
two.org
three.org

These are were the emails migrated over.

Now with COVID-19 we've moved a lot fo the cloud, including all computer to Azure AD. We have been working on enabling Azure AD Domain Services Secure , we have it up and working. This is where I thunk the error is made. We made it a .lan like the main domain. Now setting up secure ldap it looks like we need a FQDN. Any suggestions from anyone?

Thanks
Craig