Unable to create ANY new datatype in Process (OIC) using JSON import

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We're building a process application in Oracle Integration Cloud's 'Process' product. The processes we're building mainly consist of service calls to a REST API. To process the responses of the REST endpoints we created various Business Types in our process application that have the same data structure as the responses from the REST API's endpoints.

Most data types were imported by copy pasting (Create>Import Business Object>From JSON) a sample response from a REST endpoint. One Business Type 'MyBusinessType' (real name removed) was however created manually (Create>New Business Object), since no JSON example was available at the time. Today I wanted to replace this Business Type by a Business Type based on a JSON example, so we could use these for our REST calls and update the Business Type in the future by updating the JSON example, if needed.