String model references must be of the form 'app_label.ModelName' error while adding a Foreign Key field to model

I have an app customer inside company/sales/ with app_label as 'company.sales.customer'. This app contains a model Customer in models.py.

I want this model to be linked as a foreign key in another app 'orders'.

models.py of 'orders':

from django.db import models
 
class Order(models.Model):
    party = models.ForeignKey('company.sales.customer.Customer', on_delete=models.CASCADE)
    --other fields--

apps.py of 'customer':

from django.apps import AppConfig


class CustomerConfig(AppConfig):
    name = 'company.sales.customer'
    label = 'company.sales.customer'

settings.py :

INSTALLED_APPS = [
----,
'company.sales.customer'
]

On running python manage.py makemigrations, I get this error :

ValueError: Invalid model reference 'company.sales.customer.Customer'. String model references must be of the form 'app_label.ModelName'.