def ok_tags(tags: dict) -> bool:
        """
        Whether input tags dict is OK as an indy-sdk tags structure (depth=1, string values).
        """

        if not tags:
            return True
        depth = 0
        queue = [(i, depth+1) for i in tags.values() if isinstance(i, dict)]
        max_depth = 0
        while queue and max_depth < 2:
            sub, depth = queue.pop()
            max_depth = max(max_depth, depth)
            queue = queue + [(i, depth+1) for i in sub.values() if isinstance(i, dict)]

        return max_depth < 2 and all(isinstance(k, str) and isinstance(tags[k], str) for k in tags)
Whether input tags dict is OK as an indy-sdk tags structure (depth=1, string values).