Multidatastream creation gives error 400. Property 'unitOfMeasurements' must be non-NULL

[yaroslavtsevam]

The code below gives error. ERROR:root:Creating MultiDatastream failed with status-code 400, Property 'unitOfMeasurements' must be non-NULL.

import frost_sta_client as fsc
uplink_data_example =  {'deduplicationId': 'd7fa29e4-9278-4930-85da-061f058c8bd8', 'time': '2025-08-14T17:51:23.556259682+00:00', 'deviceInfo': {'tenantId': '52f14cd4-c6f1-4fbd-8f87-4025e1d49242', 'tenantName': 'ChirpStack', 'applicationId': '7c3f2d19-f944-4174-90d5-92d01cdc5b41', 'applicationName': 'TT-Cyber', 'deviceProfileId': 'e73da284-f29c-491f-87ba-8f3189e35b36', 'deviceProfileName': 'TT-Cyber', 'deviceName': '8123A057', 'devEui': 'ac1f09fffe0d6ccf', 'deviceClassEnabled': 'CLASS_A', 'tags': {}}, 'devAddr': '01999cae', 'adr': True, 'dr': 5, 'fCnt': 3, 'fPort': 2, 'confirmed': False, 'data': 'Z6AjgQY/MQQAAwAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA==', 'rxInfo': [{'gatewayId': 'fc97314547544166', 'uplinkId': 42933, 'nsTime': '2025-08-14T17:51:23.345709465+00:00', 'rssi': -94, 'snr': 11.8, 'channel': 2, 'location': {'latitude': 65.6497228, 'longitude': 67.501316475984694}, 'context': 'ECvQwQ==', 'metadata': {'region_config_id': 'eu868', 'region_common_name': 'EU868'}, 'crcStatus': 'CRC_OK'}], 'txInfo': {'frequency': 868500000, 'modulation': {'lora': {'bandwidth': 125000, 'spreadingFactor': 7, 'codeRate': 'CR_4_5'}}}}
service_url_ex = "http://some_url/frost/v1.1"
service = fsc.SensorThingsService(service_url_ex)
serial_num =  uplink_data_example['deviceInfo']['deviceName']
thing_id = "TTCyberSN" + serial_num
ds_id    = f"MDSTTC{serial_num}Meteo"
ds_name  = f"mds_ttc_sn_{serial_num}_meteo"
thing_id = "TTCyberSN" + serial_num
tt_thing = service.things().find(id=thing_id)
sns_meteo= service.sensors().find(id="SnsTTCMeteo")
op_unix  = service.observed_properties().find(id="OPUnixTime")
op_airtemp= service.observed_properties().find(id="OPAirTempCel")
op_airrh = service.observed_properties().find(id="OPAirRH")
op_airvpd= service.observed_properties().find(id="OPAirVPD")
mds_meteo= fsc.MultiDatastream(
    id=ds_id,
    name=ds_name,
    description="TTCyber meteorological data (air temperature, RH, VPD)",
    observation_type="http://www.opengis.net/def/observationType/OGC-OM/2.0/OM_ComplexObservation",
    multi_observation_data_types = [
        "http://www.opengis.net/def/observationType/OGC-OM/2.0/OM_Measurement",
        "http://www.opengis.net/def/observationType/OGC-OM/2.0/OM_Measurement",
        "http://www.opengis.net/def/observationType/OGC-OM/2.0/OM_Measurement",
        "http://www.opengis.net/def/observationType/OGC-OM/2.0/OM_Measurement"
    ],
    unit_of_measurements=[
        fsc.UnitOfMeasurement(name="Seconds",  symbol="s",   definition="Unix time"),
        fsc.UnitOfMeasurement(name="Celsius",  symbol="°C",  definition="Air temperature"),
        fsc.UnitOfMeasurement(name="Percent",  symbol="%",   definition="Relative humidity"),
        fsc.UnitOfMeasurement(name="kPa",      symbol="kPa", definition="Vapour Pressure Deficit")
    ],
    thing = tt_thing,
    sensor = sns_meteo,
    observed_properties = [op_unix, op_airtemp, op_airrh, op_airvpd]
)
service.create(mds_meteo)

[yaroslavtsevam]

Little update. I dug a little bit deeper and found out that, multidatastream object can give it json representation with .getstate() .I checked on my objects and they really have 'None' in 'UnitOfMeasurements':
{'@iot.id': 'MDSTTC8123A057Meteo', 'name': 'mds_ttc_sn_8123A057_meteo', 'description': 'TTCyber meteorological data (air temperature, RH, VPD)', 'observationType': '[http://www.opengis.net/def/observationType/OGC-OM/2.0/OM_ComplexObservation](vscode-file://vscode-app/Applications/Positron.app/Contents/Resources/app/out/vs/code/electron-browser/workbench/workbench.html#)', 'Thing': {'@iot.id': 'TTCyberSN8123A057', 'name': 'ttc_sn_8123A057', 'description': 'This is TTCyber device', 'properties': {'currentfoiid': 'FoIUniversalTemporary', 'eui': 'ac1f09fffe0d6c73', 'firmware': 'Unknown', 'gatewayid': 'fc97314675547544166', 'islora': 'True', 'owner': 'Unknown'}}, 'Sensor': {'@iot.id': 'SnsTTCMeteo', 'name': 'sns_ttc_meteo', 'description': 'TTCyber meteorological sensor data', 'properties': {'stringvariables': ['unix-datetime', 'airt', 'RH', 'VPD']}, 'encodingType': 'application/pdf', 'metadata': '[http://example.org/](vscode-file://vscode-app/Applications/Positron.app/Contents/Resources/app/out/vs/code/electron-browser/workbench/workbench.html#)'}, 'unitOfMeasurements': None, 'multiObservationDataTypes': ['[http://www.opengis.net/def/observationType/OGC-OM/2.0/OM_Measurement](vscode-file://vscode-app/Applications/Positron.app/Contents/Resources/app/out/vs/code/electron-browser/workbench/workbench.html#)', '[http://www.opengis.net/def/observationType/OGC-OM/2.0/OM_Measurement](vscode-file://vscode-app/Applications/Positron.app/Contents/Resources/app/out/vs/code/electron-browser/workbench/workbench.html#)', '[http://www.opengis.net/def/observationType/OGC-OM/2.0/OM_Measurement](vscode-file://vscode-app/Applications/Positron.app/Contents/Resources/app/out/vs/code/electron-browser/workbench/workbench.html#)', '[http://www.opengis.net/def/observationType/OGC-OM/2.0/OM_Measurement](vscode-file://vscode-app/Applications/Positron.app/Contents/Resources/app/out/vs/code/electron-browser/workbench/workbench.html#)'], 'ObservedProperties': [{'@iot.id': 'OPUnixTime', 'name': 'op_unix_time', 'description': 'EPOC Unix time', 'definition': '[https://www.fakedifinitions.site](vscode-file://vscode-app/Applications/Positron.app/Contents/Resources/app/out/vs/code/electron-browser/workbench/workbench.html#)', 'properties': {'category': 'processed'}}, {'@iot.id': 'OPAirTempCel', 'name': 'op_air_temp_cels', 'description': 'Data about air temperature in celsius', 'definition': '[https://www.fakedifinitions.site](vscode-file://vscode-app/Applications/Positron.app/Contents/Resources/app/out/vs/code/electron-browser/workbench/workbench.html#)', 'properties': {'category': 'processed'}}, {'@iot.id': 'OPAirRH', 'name': 'op_air_rh', 'description': 'Data about air relative humidity in percents', 'definition': '[https://www.fakedifinitions.site](vscode-file://vscode-app/Applications/Positron.app/Contents/Resources/app/out/vs/code/electron-browser/workbench/workbench.html#)', 'properties': {'category': 'processed'}}, {'@iot.id': 'OPAirVPD', 'name': 'op_air_vpd', 'description': 'Data about air vapour pressure deficit in kPa', 'definition': '[https://www.fakedifinitions.site](vscode-file://vscode-app/Applications/Positron.app/Contents/Resources/app/out/vs/code/electron-browser/workbench/workbench.html#)', 'properties': {'category': 'processed'}}]}