Function App DNS Resolution

Hi, 

 

I'm fairly new to Azure, having an issue with a function app that I've written. Its a fairly basic http c# trigger that goes away to a IIS site hosted (on a VM) inside the same Azure account and gets a response.

 

I've created a DNS Zone inside the resource group, with an 'a' record for the server hosting the IIS server, however the function app can't resolve the dns entry it's being pointed at (the a record).

 

Any tips would be greatly received.  

 

Regards,

 

Chris