SAML service provider without entity ID field

Good Afternoon, I hope someone can understand and answer my question.
Our Application was built for Auth0 and allows Enterprise SAML connections to be created. The application works correctly when we setup the Service provider with Google Admin console SAML or Microsoft Azure SAML. With both of these, when creating the integration you must add the Entity ID which we have provided in our documentation.
However one of our customers built their own SAML SP and he can not use the SAML integration. I noticed that when he is setting up the SAML SP, he does not have a field to enter in the Entity ID. He Claims this is not needed however based on my research this is a required field so I am not sure how his other SAML integrations are working.