You have noticed that standard field "MarketingLeadIndicator" is missing from the ContactCollection in OData v2 (c4codataapi) compared to the same collection in the defunct v1 OData (c4codata).
SAP Cloud for Customer
The ContactCollection already only displays records with "MarketingLeadIndicator" set as false, so it's unnecessary to expose this field in the metadata. It was visible in the ContactCollection of c4codata as a mistake, so this was corrected for the new c4codataapi service, where the field is now hidden.
This is the standard system behavior.
ContactCollection, MarketingLeadIndicator, OData , KBA , LOD-CRM-CON , Contact , LOD-CRM-INT-API , OData API (C4C Only) , Problem