Hi,
ZAPPL is a Navigation object for 0CUST_0MAT and ZAPPL is a customized field.
1.Check in RSA3 for data and data source whether this field is added in ECC side or not.
2. Check transformation Rule type.
3. Check table for Navigation table and object Routine.
| RSDATRNAV | Navigation Attributes |
| RSDATRNAVT | Navigation Attributes |
| RSTRAN | Transformati e information (routine ID start/end/expert) |
| RSTRANROUTMAP | Mapping of routines in Transformation (RSAABAP) |