Descriptive flexfield block.field value in API

I am creating/updating AR transaction via API. The dff is setup such way that it uses  block.field value like

CURRENCY_CODE = :TGW_HEADER.INVOICE_CURRENCY_CODE_MIR

inventory_item_id = :TLIN_LINES.INVENTORY_ITEM_ID

and organization_id =:$PROFILES$.ORG_ID

In my API call i am sending like l_trx_lines_tbl(1).ATTRIBUTE1:='USD';

The API returns error - "Error in Lines: The entered values for the descriptive flexfield are invalid. INVALID_VALUE:RA_CUSTOMER_TRX_LINES "

Anybody has a solution for it.

Thank you in advance