Database design two tables have One2One connection with another - django - models

I'm working on a project which has several models but two of them are Invoice and the other for Payment, in the both tables should have a field named next_payment for the loaners to determine when he/she should pay his/her loan

class Payment(models.Model):
    admin = models.ForeignKey(User,on_delete=models.CASCADE)
    price = models.DecimalField(max_digits=20,decimal_places=3)
    #others

class Invoice(models.Model):
    seller = models.ForeignKey(User,on_delete=models.PROTECT)
    customer = models.CharField(max_length=50)
    #others

should i add new fields named next_payment for both two models or create a new model , something like this

class NextPayment(models.Model):
    next_payment = models.DateTimeField()

and add NextPayment has OneToOne connection for two both models ? which one is the most effective way please ? thank you in advance ..

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