Unique device identifiers like IMEI have been blocked or obfuscated from at least Android 10 and higher. Only certain privileged system apps and DPCs have access to that sort of information. I'm not sure how you're problem is specific to A13 or those specific Zebra models with that in mind. On Zebra devices specifically there are at least some options to query unique device identifiers from Zebra services on device that do have the necessary permission to read those values on your behalf. They can also be passed to you from an EMM agent through Managed Configurations if you set things up correctly. In general however there are increasing restrictions on these unique device identifiers and it has therefore required some extreme workarounds in some cases if you really need them.