Custom Field value is not picked up by SAP21 Customer Invoice Form

I'm doing implementation successful S/4 Public Cloud Edition.

I've created a customized tract successful concern discourse 'FINS_JOURNAL_ENTRY_ITEM' and implemented customized logic 'FIN_ACDOC_EXT_CHG_SUBSTITUTION' to populate the said customized field. I've had enabled the usage of the customized tract to the customized signifier template.

Though customized tract is recognized by signifier template and has been bound successful a signifier field, worth is not picked up erstwhile doing a signifier preview successful Create Correspondence App.

Any steps I missed connected wherefore this is happening?