Create Entity service gives error

I’m trying to add entity services to my integration. But every time I try to call the service I’m getting a stack trace.

Error handling message: Unknown error
Traceback (most recent call last):
  File "/workspaces/ha-core/homeassistant/components/websocket_api/decorators.py", line 25, in _handle_async_response
    await func(hass, connection, msg)
  File "/workspaces/ha-core/homeassistant/components/websocket_api/commands.py", line 525, in handle_execute_script
    await script_obj.async_run(msg.get("variables"), context=context)
  File "/workspaces/ha-core/homeassistant/helpers/script.py", line 1219, in async_run
    await asyncio.shield(run.async_run())
  File "/workspaces/ha-core/homeassistant/helpers/script.py", line 353, in async_run
    await self._async_step(log_exceptions=False)
  File "/workspaces/ha-core/homeassistant/helpers/script.py", line 371, in _async_step
    await getattr(self, handler)()
  File "/workspaces/ha-core/homeassistant/helpers/script.py", line 571, in _async_call_service_step
    await service_task
  File "/workspaces/ha-core/homeassistant/core.py", line 1446, in async_call
    processed_data = handler.schema(service_data)
  File "/usr/local/lib/python3.9/site-packages/voluptuous/schema_builder.py", line 272, in __call__
    return self._compiled([], data)
  File "/usr/local/lib/python3.9/site-packages/voluptuous/validators.py", line 215, in _run
    return self._exec(self._compiled, value, path)
  File "/usr/local/lib/python3.9/site-packages/voluptuous/validators.py", line 339, in _exec
    v = func(path, v)
  File "/usr/local/lib/python3.9/site-packages/voluptuous/schema_builder.py", line 817, in validate_callable
    return schema(data)
  File "/workspaces/ha-core/homeassistant/helpers/config_validation.py", line 134, in validate
    raise vol.Invalid("must contain at least one of {}.".format(", ".join(keys)))
TypeError: sequence item 0: expected str instance, Optional found

The only code I added was in sensor.py (the last lines)

async def async_setup_entry(
    hass: HomeAssistant, config: ConfigEntry, async_add_entities, discovery_info=None
):
    """Call the Renson integration to setup."""

    renson_api: renson.RensonVentilation = hass.data[DOMAIN][config.entry_id]

    entities: list = []
    for description in sensor_descriptions:
        entities.append(RensonSensor(description, renson_api))
    async_add_entities(entities)

    platform = entity_platform.async_get_current_platform()

    platform.async_register_entity_service(SERVICE_SYNC_TIME, {}, "sync_time")

And in the SensorEntity I added a function:

@callback
    async def sync_time(self, **kwargs):
        """Call sync time on Renson device."""
        self.renson_api.sync_time()

I cannot find what I’m doing wrong and the developer documentation does also not saying much about entity services. Can someone help me finising my first integration in hass?