Typescript: How to post a nested object to Firestore?

Question

I want to do a post with a nested object to Firestore.

Here I have an interface Project with overview inside:

interface Project {
    projectName: string,
    projectType: string,
    country: string,
    city: string,

    overview: {
      mainProject: string,
      projectId: number,
      m_tool_Id: string,
      businessUnitId: string
    }
} 

And here is my interface Request:

interface Request {
  body: Project,
  params: { projectId: string }
}

I tried to add overview to const in *addProject* and to projectObject like I added projectName, projectType, country, city, but I still could write everything inside overview. By that I mean that instead of these fields: mainProject, projectId, m_tool_Id, businessUnitId which I thought were required, I could paste any information.

const addProject = async (req: Request, res: Response, next: NextFunction) => {
  // tried to add *overview* here
  const { projectName,  projectType, country, city } = req.body 
  try {
    const project = firestore.collection('projects').doc()
    const projectObject = {
      id: project.id,
      projectName,
      projectType,
      country,
      city
    }

    project.set(projectObject)

    res.status(200).send({
      status: 'success',
      message: 'project added successfully',
      data: projectObject
    })
  } catch (error) {
    next(error);
  }
}

The goal was to get something like this in Firestore:

How can I get and require fields from a nested object and how to post them with the main object?

Sorry if that was too much info, but I just want to learn how to handle nested objects.