putSql exception

Hi,

I tried to insert some data in postgresql db using PUTSQL processor.

Below example of sql statement in putSql properties:

INSERT INTO myTable(date_response, success, code, payload_response) values ('${now()}', '${status:toNumber()}', '${code:toNumber()}', ${payload});

 The problem is when this insert is executed, i have this error:

org.postgresql.util.PSQLException: ERROR: column "zxlbavuzvmlvm2x6vedsemrdstzjrnnnzxlbavuzvmlvm2x6swpvz2v5qwlhv1f" does not exist.

What happen ? .... the payload_response column name is replace by the value of my flow file attribute ${payload}. Why ? any hints ?