Add default_auto_field and migration.

invitations/apps.py

@@ -4,5 +4,6 @@
 class Config(AppConfig):
     """Config."""
 
+    default_auto_field = "django.db.models.BigAutoField"
     name = "invitations"
     label = "invitations"

invitations/migrations/0004_auto_20230328_1430.py

@@ -0,0 +1,26 @@
+# Generated by Django 3.2.15 on 2023-03-28 14:30
+
+from django.conf import settings
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+        ('invitations', '0003_auto_20151126_1523'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='invitation',
+            name='id',
+            field=models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID'),
+        ),
+        migrations.AlterField(
+            model_name='invitation',
+            name='inviter',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.CASCADE, to=settings.AUTH_USER_MODEL, verbose_name='inviter'),
+        ),
+    ]