NeverBounce's validation action only accepts a single email address per input. [1] For comma-separated emails, you'd need to use Debounce instead, which can handle multiple email addresses in one input - either comma-separated or as an array. [2]
If you want to stick with NeverBounce, you'll need to split your comma-separated emails into individual rows first, then validate each one separately.
If you need any more help with email validation or handling comma-separated emails, please let me know. Would you like to share more about what you're trying to achieve or any specific challenges you're facing?