Sync SOAP to Proxy with BPM

Hi Experts,

I'm trying to create a BPM (in PI 7.1) which validates (by JAVA class) the XML message received and sends to R/3 an error message in case the request message isn't valid or an transformation of the request message in the other case.

The response message is either determined by a transformation mapping (when the XML is not valid) or by the R/3 after receiving and validating the contents of the request message.

I do this a lot with asynchronous scenarios but it's the first time I'm trying with sync interfaces and unfortunally I'm not managing to implement this.

Is this possible? Is there any better way of doing this without BPM? Do you need more information?

Thank you all in advance.