I did a workaround and run this command using a bash script. When I try to send this json as a parameter I had the same error. I imagine that is not a problem from Nifi, but something related to passing a json to a bash script. In my processor I run the script and as parameter the name of my function and the url to search. To solve the problem of the json I create a temporary file with the data.    #!/bin/bash TABLE="myTable" URL=$2 FILTER_EXPRESSION="url = :value" EXPRESSION_ATTR="{\":value\":{\"S\":\"$URL\"}}" endpoint () { echo $EXPRESSION_ATTR > /tmp/expression.json aws dynamodb scan --table-name $TABLE \ --filter-expression "$FILTER_EXPRESSION" \ --expression-attribute-values file:///tmp/expression.json \ rm -f /tmp/expression.json } $1   ... View more