Need help in identifying the right ip needed to whitelist

Hi Devs, I need to know which IP to use if I need to whitelist my services in an external applications/websites

example: my EKS is hosting multiple micro services and one of this needs to call api of external services provider, but need to whitelist ip in this external service provide if I need my pod/services needs to call the apis of the external service,

I have VPC around the EKS prod cluster with Public ip for Master node

am confused on which IP should i use to whitelist the pod in external service, help much appreciated. tried whitelisting the master node public ip , no luck I can successfully call apis from master node, but when micro service calls it , it gets blocked because of un authorised ip error.