Show only one field in Django Admin panel?

Question

I have the following two classes declared in admin Django files. On the admin panel 3 inline inputs are shown, I only want to show 1 input. Any guesses on why 3 inline inputs are shown instead of just one?

class OriginURLInline(ViewPermissionMixin, admin.StackedInline):
model=IncentiveReferrerURL
verbose_name = 'Promotion URL'
verbose_name_plural = 'Promotion link'
fields = ('origin_url',)

class IncentiveReferrerURL(TimeStampedModel):
# The TimeStampedModel will provide self-updating 'created' and 'modified' fields on the inherited model

incentive = models.ForeignKey(
    Incentive,
    on_delete=models.PROTECT,
    null=True,
    blank=True,
)
origin_url = models.CharField(
    max_length = 100,
    verbose_name = 'Promotion Name:',
    help_text='Please e'
)

Answer 1

On your admin add:

extra=0

that will fix this behavior