QUERY_TASK_ATTACHMENTS is not implemented

Hello,

I set up a FIORI my inbox.

When a open a Task with an attachment I receive following Error Message:

<code>/IWBEP/CX_MGW_TECH_EXCEPTION</code>

<message>Method 'QUERY_TASK_ATTACHMENTS' is not implemented.</message>

When I send a GET-Request with this header:

/sap/opu/odata/IWPGW/TASKPROCESSING;mo;v=2/TaskCollection(SAP__Origin='LOCAL',InstanceID='abc61da8418c11e59b53000034a3254e')/Attachments/$count?sap-client=100

I receive an error message stating:

Ressource not found for Segment 'TaskCollection'

Installed:

Do I missed a service or something else ?

Kind regards