Are the IP address of my web-app dynamic

I have my flask app running as always-on task , I am facing some issue with a client API , they are asking if the server has dynamic API ? Can you please give me some details about it ?

Yes, the IP may vary -- we have a help page on that:

In the "The excessive whitelist" section , I can see if we want to whitelist all IPs (aws) , It mentions - "you can consider whitelisting all of Amazon's us-east-1 datacenter". Considering this is , that region should change for us right ? , instead of us-east-1 it should be europe region.

Yes, that would be "eu-central-1" (but it's not recommended).