Trying to make sense of InvalidInputException

Full Exception:

InvalidInputException: An error occurred (InvalidInputException) when calling the CreateDatasetImportJob operation: Input csv has rows that do not conform to the dataset schema. Please ensure all required data fields are present and that they are of the type specified in the schema.

I am trying to create an interactions dataset import job in Amazon Personalize from Amazon SageMaker. My interactions schema looks like this:

interactions_schema = {"type" : "record", 
                       "name" : "Interactions",
                       "namespace" : "com.amazonaws.personalize.schema",
                       "fields" : [{"name" : "ITEM_ID",
                                    "type" : "string"},
                                   {"name" : "USER_ID",
                                    "type" : "string"},
                                   {"name" : "TIMESTAMP",
                                    "type" : "float"},
                                   {"name" : "EVENT_VALUE",
                                    "type" : "long"},
                                   {"name" : "EVENT_TYPE",
                                    "type" : "string"}],
                       "version" : "1.0"}

The only thing I can think of that could lead to the above exception is that when I save my CSV to my S3 bucket, the fields with type 'string' get saved as type 'object'. Otherwise not sure what I could be doing wrong.

Edit: I have now tried the following:

interactions_schema = {"type" : "record", 
                       "name" : "Interactions",
                       "namespace" : "com.amazonaws.personalize.schema",
                       "fields" : [{"name" : "ITEM_ID",
                                    "type" : "string"},
                                   {"name" : "USER_ID",
                                    "type" : "string"},
                                   {"name" : "TIMESTAMP",
                                    "type" : "long"},
                                   {"name" : "EVENT_VALUE",
                                    "type" : "float"},
                                   {"name" : "EVENT_TYPE",
                                    "type" : "string"}],
                       "version" : "1.0"}