I have this client schema that has a reference to a progress schema. I keep getting an error when I run the code. I think my syntax is wrong in the validation method, but not sure of the correct syntax for validate reference documents...any ideas??

Error:

UnhandledPromiseRejectionWarning: Error: Schema can only contain plain objects

const clientSchema = new Schema(
  {
    name: {
      type: String,
    },
    contactDetails: contactSchema,
    addressDetails: addressSchema,
    clientGoals: {
      type: String,
    },
    progressUpdates: [
      {
        type: Schema.Types.ObjectId,
        ref: "Progress",
      },
    ],
  },
  {
    // Define collection name
    collection: "clients",
  }
);

const Client = mongoose.model("Client", clientSchema);

// Validation using Joi
function validateClient(client) {
  const schema = Joi.object({
    name: Joi.string().min(3).required(),
    contactDetails: {
      email: Joi.string().required(),
      contactNumber: Joi.string().required(),
    },
    addressDetails: {
      number: Joi.number().integer().required(),
      street: Joi.string().required(),
      city: Joi.string().required(),
    },
    clientGoals: Joi.string().min(5).required(),
    progressUpdates: Joi.array().items(
      Joi.object().keys(progressSchema).required()
    ),
  });
  return schema.validate(client);
}

progressSchema

 const progressSchema = new mongoose.Schema(
      {
        content: {
          type: String,
        },
        client: {
          type: Schema.Types.ObjectId,
          ref: "Client",
        },
      },
      {
        // Define collection name
        collection: "progress",
      }
    );