Connection between AWS AppFlow and SAP OData fails with error 400 (certificate issue?)

Hi all, We are currently facing some issues with connecting our on-premises SAP system to AWS via AWS AppFlow. We decided to use the OData interface as described here in the official AWS documentation. The interface (for now) is publicly accessible and can be called via Postman for example. When we try to set up the connection via AWS Appflow we receive the following error:

Error while communicating to connector: Client error: The request to SAP failed with the status code: 400 and error message: Unable to find valid certification path to requested target and response: (Service: SandstoneBridgeService; Status Code: 400; Error Code: ConnectorClientException; Request ID: b54c78ce-1264-401c-b889-81b1252f3a8c; Proxy: null)

On the common errors page for AppFlow I can't find this error and also searching community forums didn't really help so far. Has anyone ever experienced this problem or has any suggestion how to resolve this? Any help is very much appreciated.

Thanks in advance! Patrick