I can't guarantee I will be able to help as I haven't had much exposure to ATM configuration, but still, I would need to see your configuration including the command you are trying to add, including the result of addition of that command.
I hope you have checked the log of the router when you apply this "service-policy" command on the ATM interface. The reason why I say this is because for ATM interface, based on whether the policy has shaping configured or not, we have to use vbr-nrt and then it is accepted
check this Cisco document "Where Do I Apply a QoS Service Policy on an ATM Interface?"
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...