With transaction RSFLAT you can emulate exactly the same query and verify the datastream you woulg get in Crystal Reports. This transaction is useful when you want to see what data a BEx query will return.
Use transaction SE37 to call the OLAP BAPI function manually so that you can verify the metadata retrieved by Crystal Reports. You can see OLAP BAPI calls in SAP integration trace. Please refer to section 8.3.1 of [Web Intelligence on SAP implementation best practices]
Use transaction RSRTRACE to create an OLAP trace on the SAP BW server. Please refer to section 8.3.2 of [Web Intelligence on SAP implementation best practices]