pyFlink UDTF function registration

[Manas Kale]

Hi,
I am trying to use a UserDefined Table Function to split up some data as
follows:

from pyflink.table.udf import udtf

@udtf(input_types=DataTypes.STRING(), result_types=
[DataTypes.STRING(), DataTypes.DOUBLE()])
def split_feature_values(data_string):
    json_data = loads(data_string)
    for f_name, f_value in json_data.items():
        yield (f_name, f_value)

# configure the off-heap memory of current taskmanager to enable the
python worker uses off-heap memory.
t_env.get_config().get_configuration().set_string("taskmanager.memory.task.off-heap.size",
'80m')

# Register UDTF
t_env.register_function("split", split_feature_values)
ddl_source = f"""
    CREATE TABLE {INPUT_TABLE} (
        `monitorId` STRING,
        `deviceId` STRING,
        `state` INT,
        `data` STRING,
        `time_st` TIMESTAMP(3),
        WATERMARK FOR time_st AS time_st - INTERVAL '2' SECOND
    ) WITH (
        'connector' = 'kafka',
        'topic' = '{INPUT_TOPIC}',
        'properties.bootstrap.servers' = '{LOCAL_KAFKA}',
        'format' = 'json'
    )
"""

ddl_temporary_table = f"""
    CREATE TABLE {TEMPORARY_TABLE} (
        `monitorId` STRING,
        `featureName` STRING,
        `featureData` DOUBLE,
        `time_st` TIMESTAMP(3),
        WATERMARK FOR time_st AS time_st - INTERVAL '2' SECOND
    )
"""

ddl_populate_temporary_table = f"""
    INSERT INTO {TEMPORARY_TABLE}
    SELECT monitorId, split(data), time_st
    FROM {INPUT_TABLE}
"""

t_env.execute_sql(ddl_source)
t_env.execute_sql(ddl_temporary_table)
t_env.execute_sql(ddl_populate_temporary_table)


However, I get the following error :
py4j.protocol.Py4JJavaError: An error occurred while calling o5.executeSql.
: org.apache.flink.table.api.ValidationException: SQL validation failed.
>From line 3, column 23 to line 3, column 33:* No match found for function
signature split(<CHARACTER>)*

I believe I am using the correct call to register the UDTF as per [1]. Am I
missing something?

Thanks,
Manas

[1]
https://ci.apache.org/projects/flink/flink-docs-release-1.11/dev/table/python/python_udfs.html#table-functions