REST response needs to use property qualifier pzExternalName
As a developer on 7.1.7, you need to control the mapping between JSON element names and property names in Pega. You have added a property qualifier named "pzExternalName" on one of the target properties in Pega but Designer Studio is not allowing the save.
Steps to Reproduce
From advanced tab of Edit Property rule form for property named "sampleProp", add a new qualifier named "pzExternalName" and set it to the JSON element named expected in responses being mapped.
The pzExternalName functionality was introduced in Pega 7.1.8 but is available to 7.1.7 through a hotfix.
Apply HFix-26838 and restart server.