[credit card] implement payment

uncloud_pay/migrations/0008_payment_external_reference.py

@@ -0,0 +1,18 @@
+# Generated by Django 3.1 on 2020-12-29 00:04
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('uncloud_pay', '0007_auto_20201228_2338'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='payment',
+            name='external_reference',
+            field=models.CharField(default='', max_length=256),
+        ),
+    ]