You have created a Web Service Mashup to use with a Data Mashup, however you are not able to preview the data and receive Error 500.
SAP Cloud for Customer
One of the possibilities is due to the service protocol set to JSON. We do not support JSON as a service protocol for Data Mashup.
You should use XML as a service protocol.
data mashup, preview, REST, web service , KBA , data mashup , AP-RC-GEN-MSH , Mashups , How To