Adding a Second IP Address

We are looking to migrate an application which requires two private IP addresses. Azure has assigned my VM IP Address 10.99.99.8 via DHCP.

I statically assign a second unused IP 10.99.99.108 to the NIC in the advanced settings so both 10.99.99.8 and 108 are assigned to the same NIC.

However the 108 address is not pingable by any other hosts.

Is there a supported method to add a second IP?  An unsupported method?

Thanks!