My joi validation is throwing an error when submitting a form. The error message reads:

STACK: Error: "author.surname" is not allowed at module.exports.citationJoi

As far as I can tell my joiSchema is ok:

const nestedScehma = Joi.object().keys({
    surname: Joi.string().trim().required(),
    firstname: Joi.string().trim().required()
  })

  
module.exports.citationJoi = (req, res, next) => {
  const memberSchema = Joi.object().keys({
    quote: Joi.string().trim().required(),
    author: nestedScehma,
    page: Joi.string().allow(null, '').trim(),
    year: Joi.string().allow(null, '').trim(),
    title: Joi.string().allow(null, '').trim(),
    publisher: Joi.string().allow(null, '').trim(),
    place: Joi.string().allow(null, '').trim()
  })

  const { error } = memberSchema.validate(req.body);
  if(error) {
    const msg = error.details.map(el => el.message).join(",");
    throw new AppError(msg, 400);
  } else {
    next();
  }
}

Which relates to my Mongoose Schema:

const quoteScheme = new Schema({
    quote: {
        type: String,
        required: true
    },
    author: {
        surname: {
            type: String,
            required: true
        },
        firstname: {
            type: String,
            required: true
        }
    },
    page: {
        type: String,
        required: false
    },
    year: {
        type: String,
        required: false
    },
    title: {
        type: String,
        required: false
    },
    publisher: {
        type: String,
        required: false
    },
    place: {
        type: String,
        required: false
    }

})

I have been stuck here for a while now and the only oddity (to my newbie mind at least) is that in the req.body has added quotations to the author.surname and author.firstname keys:

{
  quote: "Ozzy Osbourne's advice on how rock stars should treat young bands is wholesome as heck",
  'author.surname': 'tosser',
  'author.firstname': 'Oscar',
  page: '',
  year: '',
  title: '',
  publisher: '',
  place: ''
}

The name attribute on the input is "author.surname" relating to the Mongoose schema. I presume that somewhere along the way quotation marks have been added to the key as a reaction to the dot notation resulting in Joi throwing an error? Am I on the right lines? How can I fix this? Many thanks.