An Autonomous Database with the workload type Data Warehouse, Transaction Processing, JSON or APEX is a prerequisite of running APEX on an Autonomous Database. According to the Oracle documentation, “Oracle Application Express (APEX) is a low-code development platformthat enables you to build scalable, secure apps with world-class features that can be deployed anywhere. APEX is preconfigured and fully managed in Oracle Autonomous Database (ADB). You can use APEX on any Autonomous Database workload type: Data Warehouse (ADW), Transaction Processing (ATP), JSON (AJD), or APEX (APEX).”