An Azure service that is used to provision Windows and Linux virtual machines.
Classic VMs are going out of support in March this year: https://learn.microsoft.com/en-us/azure/virtual-machines/classic-vm-deprecation
You need to get these converted to ARM, ASAP!
How does this affect me? As of February 28, 2020, customers who didn't utilize IaaS VMs through ASM in the month of February 2020 can no longer create VMs (classic). On March 1, 2023, customers will no longer be able to start IaaS VMs by using ASM. Any that are still running or allocated will be stopped and deallocated. On March 1, 2023, subscriptions that are not migrated to Azure Resource Manager will be informed regarding timelines for deleting any remaining VMs (classic).
In regards to creating a Public IP for the Classic VM - you could try the article below which relies on an old Azure PowerShell module: https://www.damirscorner.com/blog/posts/20160229-CreateAReservedIpForAClassicAzureVm.html
If the above steps in the article fail to work, your best bet may be to migrate it to ARM, then attach a Public IP via ARM.