Saml authentication failed with error code 100

Saml authentication failed with error code 100

Hi
I'm configuring saml idp-initiated login as a SSO solution for ServiceDesk plus version 14.3. but it gives the error "Saml authentication failed with error code 100" (error screenshot is attached ).
On this page:
There's no explanation for error code 100.
Can you please tell me the reason and resolution for this error code or at least give a hint about what is wrong.
Thanks in advance.

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