Changing Internet Service Providers (ISP) is a common business processes as internet gets upgrade. Use this article to ensure you consider the necessary things to update and have your WebAPI continue operation.
Typically the WebAPI runs on a server or workstation on your local network. Your router will typically point an external internet IP address and port provided by your ISP to this server or workstation on your internal network.
Ensure you paid for and receive a static IP address. It's called static because it doesn't change.
If your Internet Service Provider replaced your router you may need to place a call into their technical support to forward the port of your WebAPI to the workstation or server it is being hosted on.
If you have an integration partner that points to your WebAPI you will need to update them. Contact your integration partner to assist you where to enter in the new static IP address into their software.