Alias issue on a Shared IP (Not Default)

Hi there, I have a slight issue with an alias server against a non-default Shared IP address.

Against this IP, I have the following:

domain1 (this is the default website for the IP address) domain2 domain3

These all work correctly as you would expect.

I have tried to add an alias to domain2 as follows

I have updated the dns records to point to the IP address. When I access domain2a in a browser, it goes to domain1 instead of domain2.

What have I missed?

Thanks, Craig