Error posting using Ema Consumer

Also, can we continue to use MarketLink service? Is there any timeline when Marketlink is going to be obsolete?

We are testing using the example in above link under section: "Contribution through Refinitiv's Real-Time Distribution System"

We are able to receive the RefreshMsg from the target page with existing data.

Received Refresh. Item Handle: 2 Closure: com.refinitiv.ema.access.OmmConsumerImpl@fb445a3
Item Name: 1FHLBA1
Service Name: IDN_RDF
Item State: Open / Ok / None / '*All is well'
Fid: 1 Name = PROD_PERM DataType: UInt Value: 3784
Fid: 2 Name = RDNDISPLAY DataType: UInt Value: 151
Fid: 259 Name = RECORDTYPE DataType: UInt Value: 25

However when we are trying to update value of a specific field (say Fid:1) in callback method onRefreshMsg( ) using below code,

PostMsg postMsg = EmaFactory.createPostMsg();
UpdateMsg nestedUpdateMsg = EmaFactory.createUpdateMsg().streamId(refreshMsg.streamId()).name("1FHLBA1");
FieldList nestedFieldList = EmaFactory.createFieldList();
nestedFieldList.add(EmaFactory.createFieldEntry().intValue(1, 3785));
nestedUpdateMsg.payload(nestedFieldList );

((OmmConsumer)event.closure()).submit( postMsg.postId( ++postId).serviceName("DCS_MARKETLINK")

                    .name( "1FHLBA1" )

                    .solicitAck( true ).complete(true)

                    .payload(nestedUpdateMsg), event.handle() );

we get error:

Received AckMsg. Item Handle: 1 Closure: com.refinitiv.ema.access.OmmConsumerImpl@fb445a3
Item Name: 1FHLBA1
Service Name: not set
Ack Id: 2
Nack Code: DeniedBySource
Text: Unable to update fixed area of page or non-contributable field

Is this because we need to setup the update msg in a different way?

Thanks

-Parik