Help Needed - Configuration Flow - With Progress in Options Flow

I am working on Samsung SmartTag plugin. (Native, i.e. without Android App)
I have a (attached) to configure. It has an options flow.
In the options I plan to add a device and various entities when the SmartTag button is pressed.
I just use a timer task to simulare waiting for the bluetooth results.
I get an an error Dialog when completed, without any error messages in the logs.

Second question, I am currently developing in a config/custom_components directory (in order to test bluetooth on my development platform which is an odroid, supervised.
Are the strings.json and traslations supposed to work here ?

Images: Integration, Options Progress, Breakpoint in code, Options after breakpoint. Code:

"""Config flow for Samssung SmartTag integration."""
from __future__ import annotations
import asyncio
from typing import Any
from homeassistant import config_entries
from homeassistant.core import callback
from .const import DOMAIN

class ConfigFlow(config_entries.ConfigFlow, domain=DOMAIN):
    """Handle a config flow for Samsung SmartTag."""

    VERSION = 1

    async def async_step_user(self, user_input=None):
        """Handle the initial step."""
        return self.async_create_entry(title="Samsung SmartTag", data={})

    def async_get_options_flow(
        config_entry: config_entries.ConfigEntry,
    ) -> OptionsFlowHandler:
        """Return the options flow."""
        return OptionsFlowHandler(config_entry)

class OptionsFlowHandler(config_entries.OptionsFlow):
    """Handle an options flow for Samsung SmartTag."""
    def __init__(self, config_entry: config_entries.ConfigEntry) -> None:
        """Set up the options flow."""
        self.config_entry = config_entry
    async def _async_do_task(self, work):
        await work  # A task that takes some time to complete.

    async def async_step_init(self, user_input=None):
        """Handle the initial step."""
        # Simulate a task to wait for SmartTag button press
        task = asyncio.sleep(10)
        return self.async_show_progress(step_id="user", progress_action="wait")

    async def async_step_user(self, user_input=None):
        """Flow Next Step"""
        return self.async_show_progress_done(next_step_id="finish")
    async def async_step_finish(self, user_input=None):
        """Flow Finish Step"""
        # If new devices, then Create Device and Entities for device_tracker, sensors, and button
        return self.async_create_entry(title="Samsung SmartTag Options", data={})

Rebuilding the dev container and running python3 -m script.hassfest has solved the problems.