Well while you answered I tested after ringing and it is the same.
Actually the panel does not stop the ringing.
This is what happened when I pressed the answer button twice:
2023-12-10 20:16:23.743 | INFO | event:video_intercom_alarm:120 - Video intercom alarm from home_front_gate
2023-12-10 20:16:34.279 | INFO | mqtt_input:_answer_call_callback:344 - Received answer command for doorbell: main_indoor_panel
2023-12-10 20:16:34.291 | ERROR | mqtt_input:_answer_call_callback:357 - Error while answering call with ISAPI: ('Error while calling ISAPI /ISAPI/VideoIntercom/callSignal?format=json', 29, 'Device operation failed.')
[2023-12-10 20:16:34.291][DBG] SimpleSTDCommandToDvr with out cmd[PUT /ISAPI/VideoIntercom/callSignal?format=json], input size[37], max segment length[262144]
2023-12-10 20:16:35.292 | INFO | mqtt_input:_hangup_call_callback:321 - Received hangup command for doorbell: main_indoor_panel
2023-12-10 20:16:35.309 | ERROR | mqtt_input:_hangup_call_callback:334 - Error while Hanging up the call with ISAPI: ('Error while calling ISAPI /ISAPI/VideoIntercom/callSignal?format=json', 29, 'Device operation failed.')
[2023-12-10 20:16:35.309][DBG] SimpleSTDCommandToDvr with out cmd[PUT /ISAPI/VideoIntercom/callSignal?format=json], input size[37], max segment length[262144]
2023-12-10 20:16:40.023 | INFO | mqtt_input:_answer_call_callback:344 - Received answer command for doorbell: main_indoor_panel
2023-12-10 20:16:40.035 | ERROR | mqtt_input:_answer_call_callback:357 - Error while answering call with ISAPI: ('Error while calling ISAPI /ISAPI/VideoIntercom/callSignal?format=json', 29, 'Device operation failed.')
[2023-12-10 20:16:40.035][DBG] SimpleSTDCommandToDvr with out cmd[PUT /ISAPI/VideoIntercom/callSignal?format=json], input size[37], max segment length[262144]
2023-12-10 20:16:41.040 | INFO | mqtt_input:_hangup_call_callback:321 - Received hangup command for doorbell: main_indoor_panel
2023-12-10 20:16:41.053 | ERROR | mqtt_input:_hangup_call_callback:334 - Error while Hanging up the call with ISAPI: ('Error while calling ISAPI /ISAPI/VideoIntercom/callSignal?format=json', 29, 'Device operation failed.')
[2023-12-10 20:16:41.053][DBG] SimpleSTDCommandToDvr with out cmd[PUT /ISAPI/VideoIntercom/callSignal?format=json], input size[37], max segment length[262144]
2023-12-10 20:16:45.779 | INFO | mqtt_input:_hangup_call_callback:321 - Received hangup command for doorbell: home_front_gate
2023-12-10 20:16:45.897 | ERROR | mqtt_input:_hangup_call_callback:334 - Error while Hanging up the call with ISAPI: ('Error while calling ISAPI /ISAPI/VideoIntercom/callSignal?format=json', 11, 'The data sent to the device is illegal, or the data received from the device error. E.g. The input data is not supported by the device for remote configuration.')
[2023-12-10 20:16:45.897][DBG] SimpleSTDCommandToDvr with out cmd[PUT /ISAPI/VideoIntercom/callSignal?format=json], input size[37], max segment length[262144]
[2023-12-10 20:16:50.571][DBG] Alarm chan [0] recv timeout[2]!
2023-12-10 20:16:56.434 | INFO | mqtt:video_intercom_alarm:327 - Call dismissed, updating sensor
settings: mqtt=MQTT(host='core-mosquitto', port=1883, username='addons', password='WohMitahLoolee0wiethohgh3aifeiziaveiNococeikoogiehietheph9eibaed', client_name=None, tls_key=None, tls_certfile=None, tls_ca_cert=None, discovery_prefix='homeassistant', state_prefix='hmd') entity=SensorInfo(component='sensor', device=DeviceInfo(name='home_front_gate', model='DS-KD8003-IME1/EU', manufacturer='Hikvision', sw_version='V2.2.62', hw_version='0x0', identifiers='6883457568564848514573776949476985484950485048485548578282695356495554505154', connections=None, configuration_url=None), device_class=None, enabled_by_default=None, entity_category=None, expire_after=None, force_update=None, icon='mdi:bell', name='Call state', object_id='home_front_gate_call_state', qos=None, unique_id='6883457568564848514573776949476985484950485048485548578282695356495554505154-call_state', unit_of_measurement=None, state_class=None) debug=False manual_availability=True
topic_prefix: sensor/home_front_gate/Call-state
config_topic: homeassistant/sensor/home_front_gate/Call-state/config
state_topic: hmd/sensor/home_front_gate/Call-state/state
wrote_configuration: True
The fact that the ringing does not stop is what bugs me. The rest is working.