Hi, first thank you for your help.
The Relying party for this trust relationship ist configured in oxTrust.
If I turn on the Sibboleth debug log mode there will be printed the following:
```
2018-05-22 07:32:08,935 - DEBUG [org.opensaml.saml.metadata.resolver.impl.PredicateRoleDescriptorResolver:264] - Resolved 1 source EntityDescriptors
2018-05-22 07:32:08,935 - DEBUG [org.opensaml.saml.metadata.resolver.impl.PredicateRoleDescriptorResolver:275] - Resolved 1 RoleDescriptor candidates via role criteria, performing predicate filtering
2018-05-22 07:32:08,936 - DEBUG [org.opensaml.saml.metadata.resolver.impl.PredicateRoleDescriptorResolver:376] - Attempting to filter candidate RoleDescriptors via resolved Predicates
2018-05-22 07:32:08,936 - DEBUG [org.opensaml.saml.metadata.resolver.impl.PredicateRoleDescriptorResolver:398] - After predicate filtering 1 RoleDescriptors remain
2018-05-22 07:32:08,936 - DEBUG [org.opensaml.saml.common.binding.impl.SAMLMetadataLookupHandler:144] - Message Handler: org.opensaml.saml.common.messaging.context.SAMLMetadataContext added to MessageContext as child of org.opensaml.saml.common.messaging.context.SAMLPeerEntityContext
2018-05-22 07:32:08,936 - DEBUG [net.shibboleth.idp.profile.impl.WebFlowMessageHandlerAdaptor:174] - Profile Action WebFlowMessageHandlerAdaptor: Invoking message handler of type 'org.opensaml.saml.common.binding.impl.SAMLAddAttributeConsumingServiceHandler' on INBOUND message context
2018-05-22 07:32:08,936 - DEBUG [net.shibboleth.idp.profile.impl.WebFlowMessageHandlerAdaptor:195] - Profile Action WebFlowMessageHandlerAdaptor: Invoking message handler on message context containing a message of type 'org.opensaml.saml.saml2.core.impl.AuthnRequestImpl'
2018-05-22 07:32:08,936 - DEBUG [org.opensaml.saml.common.binding.impl.SAMLAddAttributeConsumingServiceHandler:130] - Message Handler: Selecting default AttributeConsumingService, if any
2018-05-22 07:32:08,937 - DEBUG [org.opensaml.saml.metadata.support.AttributeConsumingServiceSelector:186] - Resolving AttributeConsumingService candidates from SPSSODescriptor
2018-05-22 07:32:08,937 - DEBUG [org.opensaml.saml.metadata.support.AttributeConsumingServiceSelector:141] - AttributeConsumingService candidate list was empty, can not select service
2018-05-22 07:32:08,937 - DEBUG [org.opensaml.saml.common.binding.impl.SAMLAddAttributeConsumingServiceHandler:138] - Message Handler: No AttributeConsumingService selected
2018-05-22 07:32:08,937 - DEBUG [net.shibboleth.idp.saml.profile.impl.InitializeRelyingPartyContextFromSAMLPeer:132] - Profile Action InitializeRelyingPartyContextFromSAMLPeer: Attaching RelyingPartyContext based on SAML peer https://#############
2018-05-22 07:32:08,940 - ERROR [net.shibboleth.idp.relyingparty.impl.ReloadingRelyingPartyConfigurationResolver:107] - RelyingPartyResolver 'shibboleth.RelyingPartyConfigurationResolver': error looking up Relying Party: Invalid configuration.
2018-05-22 07:32:08,940 - DEBUG [net.shibboleth.idp.profile.impl.SelectRelyingPartyConfiguration:131] - Profile Action SelectRelyingPartyConfiguration: No relying party configuration applies to this request
2018-05-22 07:32:08,942 - WARN [org.opensaml.profile.action.impl.LogEvent:105] - A non-proceed event occurred while processing the request: InvalidRelyingPartyConfiguration
2018-05-22 07:32:08,943 - DEBUG [org.opensaml.saml.common.profile.logic.DefaultLocalErrorPredicate:154] - No SAMLBindingContext or binding URI available, error must be handled locally
```