These articles capture the most common use cases when customers face issues with Netscaler Products unlicensed or running in grace period due to a loss of license files.
CTX269024 - How to find Hostnames and Host ID to allocate / Modify licenses
CTX232341 - How to check whether the licensed throughput limit is reached on ADC
CTX310687 - ADC Fails To Connect To ADM for Pooled Licensing
These articles provide a list of Knowledge Base resources on how to allocate and install license files to the Netscaler Products.