B is correct because the user has not configured the Salesforce1 mobile app to use My Domain for login, which is the likely cause of the issue. The My Domain URL is used to redirect theuser to the identity provider’s login page and initiate the SP-Initiated SAML flow. If the user does not configure the Salesforce1 mobile app to use My Domain for login, they will be prompted for Salesforce credentials instead of being shown the IDP loginpage. A is incorrect because the “Redirect to Identity Provider” option has been selected in the My Domain configuration, which is not the cause of the issue. The “Redirect to Identity Provider” option determines whether users are redirected to the identity provider’s login page automatically or after clicking a button. C is incorrect because the “Redirect to Identity Provider” option has not been selected in the SAML configuration, which is not the cause of the issue. The “Redirect to Identity Provider” option determines whether users are redirected to the identity provider’s login page automatically or after clicking a button. D is incorrect because the user has been granted the “Enable Single Sign-On” permission, which is not the cause of the issue. The “Enable Single Sign-On” permission allows users to use SSO with connected apps or external systems. Verified References: [My Domain URL], [SP-Initiated SAML Flow], [Redirect to Identity Provider Option], [Enable Single Sign-On Permission]