Chris, 
I went ahead and changed the GTM container to reflect the new domain. 
I also checked their Callrail account and ran a test. However, I encountered an error. 

Firefox_Screenshot_2019-10-02T16-37-22.089Z.png 33.1 KB • Download

It seems we have more than one Java script code snippet inserted = we have to remove one.
Perhaps Isaac can do so. 
Just in case, Isaac, here is the CallRail code that should be added to their account.

--- This is the code on their Callrail page and the GTM container - 

<script type="text/javascript" src="//cdn.callrail.com/companies/843124563/c1a1080db1d7ee9ce2a5/12/swap.js"></script>

Thanks Hector. All looks ok in the GTM tag now. I see where you updated the settings. Normally this doesn't make a difference, but it will probably help us stay organized. 

For the JS issue, I think Isaac will need to resolve this. 

Hey Hector - I just tested it on my end and it ran without any error + also just to make sure I also checked in the page source and could only see one instance of Callrail code in there.

js snippet.png 71.8 KB • Download

Can you pls test again on your end? Thanks man.

Isaac, 
I don't know what happened, but it is now coming up alright on my end as well. 
Thanks for verifying for me. 
Shane, thank you also for clearing that up. I think we are all good to go now. 

Great. Thanks for confirming Hector