3491508 - How to add the custom fields in payload for Journal Entry API - SAP S/4HANA Cloud Public Edition?

Custom fields have been created and enabled the in the structure of Journal Entry - Post API and Fiori App Manage Journal Entries following blog Guidelines for Creating and Enabling Extension Field for Journal Entry API 

However, there are no values in custom fields in the posted journal entry. How to add the custom fields in payload correctly when using API like Journal Entry - Post? 

"Image/data in this KBA is from SAP internal systems, sample data, or demo systems. Any resemblance to real data is purely coincidental." 

SAP S/4HANA Cloud Public Edition

Extension Field, Custom Field, Journal Entry API, Envelope, Xmlns, YY1_, yy1, Coding block, Journal Entry Item, Market Segment, FAC_FINANCIAL_DOCUMENT_SRV_01, UI_JOURNALENTRY_MANAGE, case-sensitive , KBA , AC-INT-2CL , Accounting Interface (Public Cloud) , Problem