You have crated three custom fields for Procurement Purchasing Document, enabled it to Purchase Order GUI Application and now you want to Adapt this fields in the Purchase Order - Advanced app.
SAP S/4HANA Cloud
Reproducing the Issue
- Custom Field app
- Create a new Custom Field for Procurement Purchasing Document
- Enable it to Purchase Order GUI Application
- Access Purchase Order - Advanced app
- UI adaption isn't available
Standard behavior for SAP GUI Applications, as explained in the SAP Help Adapting UIs of SAP GUI Applications.
Create the fields and publish it in the same order that you want to show them in the Purchase Order - Advanced app.
For FIORI based applications you can easily adapt the fields, as explained in the SAP Help Adapting SAP Fiori UIs at Runtime - Key User Adaptation
UI Adaption; Purchase Order; GUI; Purchase Order Advanced; , KBA , MM-PUR-PO-GUI , Userinterface - Purchase Orders , How To