Hi, I've an application running on localhost on my ubuntu. Can you pls share what would be entity id in this case?

The app running on my localhost is SP and i'm using SF as an IDP. Right now i'm getting Error: Unable to resolve request into a Service Provider

Please explain the below point

I have application A
I have salesforce system

when user logging into application A then I it shold allow single sign on to SFDC as well.

When I am configuring details in SFDC for above ( IDP initiated login, SFDC is at service provider).

I got a field called Entity ID:

Please explain what details I need to enter on this field.
Advance Thanks