Hi, Sandra.
Please monitor Shibboleth's log with command like `tail -F /opt/idp/logs/idp-process.log`, while re-trying your authentication attempts. This should give you some hints on the cause of your problem.
You also may be interested in reading our articles on configuring SAML SSO in Gluu:
1. Description of different settings: [link](https://www.gluu.org/docs/admin-guide/saml/outbound-saml/)
2. Configuring Shibboleth SP and creating TR for it in Gluu: [link](https://www.gluu.org/docs/articles/ubuntu-shib-apache/)
3. Shibboleth's quick test: [link](https://www.gluu.org/docs/articles/test-shib2/)