client cannot get RKD data with error: 500 Internal Server Error

Client get news headline with following coding:

{"RetrieveHeadlineML_Request_1":{"HeadlineMLRequest":{"Direction":"Newer","EndTime":"2022-06-02T17:43:27","Filter":[{"MetaDataConstraint":{"Value":{"Text":"LZS"},"class":"topics"}},{"MetaDataConstraint":{"Or":{"Value":[{"Text":"CLN"},{"Text":"CDS"},{"Text":"CMN"}],"Value_typehint":["Value","Value","Value"]},"class":"products"}},{"MetaDataConstraint":{"Or":{"Value":[{"Text":"PBOC"},{"Text":"PLCY"},{"Text":"CEN"},{"Text":"MCE"},{"Text":"FED"}],"Value_typehint":["Value","Value","Value","Value","Value"]},"class":"topics"}},{"FreeTextConstraint":{"Value":{"Text":"中国汇市"},"where":"Headline"}}],"MaxCount":50,"MaxCountPerFilter":false,"StartTime":"2022-06-01T17:43:27","TimeOut":30,"maxCountWorkAround":false}}}

then, get the error as below:

500 Internal Server Error: [{"Fault":{"Code":{"Value":"s:Sender","Subcode":{"Value":"a:Gateway_Validation_RequestError"}},"Reason":{"Text":{"lang":"en-US","Value":"The property 'FreeTextConstraint' has invalid child property 'O... (409 bytes)]

but, when use below coding, there is no error.

{"RetrieveHeadlineML_Request_1":{"HeadlineMLRequest":{"Direction":"Newer","EndTime":"2022-06-02T17:50:16","Filter":[{"MetaDataConstraint":{"Value":{"Text":"LZS"},"class":"topics"}},{"MetaDataConstraint":{"Or":{"Value":[{"Text":"CLN"},{"Text":"CDS"},{"Text":"CMN"}],"Value_typehint":["Value","Value","Value"]},"class":"products"}},{"MetaDataConstraint":{"Or":{"Value":[{"Text":"PBOC"},{"Text":"PLCY"},{"Text":"CEN"},{"Text":"MCE"},{"Text":"FED"}],"Value_typehint":["Value","Value","Value","Value","Value"]},"class":"topics"}},{"FreeTextConstraint":{"Or":{"Value":[{"Text":"全球汇市"},{"Text":"中国汇市"}],"Value_typehint":["Value","Value"]},"where":"headline"}}],"MaxCount":50,"MaxCountPerFilter":false,"StartTime":"2022-06-01T17:50:16","TimeOut":30,"maxCountWorkAround":false}}}

Please advise what the reason is and how to fix it.

thanks.