diff --git a/app/service/rest.py b/app/service/rest.py
index 3de1f7c4c..60141e87e 100644
--- a/app/service/rest.py
+++ b/app/service/rest.py
@@ -93,6 +93,7 @@ from app.models import (
 from app.notifications.process_notifications import persist_notification, send_notification_to_queue
 from app.schema_validation import validate
 from app.service import statistics
+from app.service.send_pdf_letter_schema import send_pdf_letter_request
 from app.service.service_data_retention_schema import (
     add_service_data_retention_request,
     update_service_data_retention_request
@@ -650,7 +651,8 @@ def create_one_off_notification(service_id):
 
 @service_blueprint.route('/<uuid:service_id>/send-pdf-letter', methods=['POST'])
 def create_pdf_letter(service_id):
-    resp = send_pdf_letter_notification(service_id, request.get_json())
+    data = validate(request.get_json(), send_pdf_letter_request)
+    resp = send_pdf_letter_notification(service_id, data)
     return jsonify(resp), 201
 
 
diff --git a/app/service/send_notification.py b/app/service/send_notification.py
index 469cf473b..883c659dc 100644
--- a/app/service/send_notification.py
+++ b/app/service/send_notification.py
@@ -23,7 +23,6 @@ from app.models import (
     SMS_TYPE,
     EMAIL_TYPE,
     LETTER_TYPE,
-    POSTAGE_TYPES,
     NOTIFICATION_DELIVERED,
     UPLOAD_LETTERS,
 )
@@ -149,11 +148,6 @@ def send_pdf_letter_notification(service_id, post_data):
         allow_whitelisted_recipients=False,
     )
 
-    postage = post_data.get('postage')
-    if postage not in POSTAGE_TYPES:
-        message = "postage must be set as 'first' or 'second'"
-        raise BadRequestError(message=message)
-
     template = get_precompiled_letter_template(service.id)
     file_location = 'service-{}/{}.pdf'.format(service.id, post_data['file_id'])
 
@@ -188,7 +182,7 @@ def send_pdf_letter_notification(service_id, post_data):
         client_reference=post_data['filename'],
         created_by_id=post_data['created_by'],
         billable_units=billable_units,
-        postage=postage,
+        postage=post_data['postage'],
     )
 
     upload_filename = get_letter_pdf_filename(
diff --git a/app/service/send_pdf_letter_schema.py b/app/service/send_pdf_letter_schema.py
new file mode 100644
index 000000000..be9c26167
--- /dev/null
+++ b/app/service/send_pdf_letter_schema.py
@@ -0,0 +1,14 @@
+send_pdf_letter_request = {
+    "$schema": "http://json-schema.org/draft-04/schema#",
+    "description": "POST send uploaded pdf letter",
+    "type": "object",
+    "title": "Send an uploaded pdf letter",
+    "properties": {
+        "postage": {"enum": ["first", "second"]},
+        "filename": {"type": "string"},
+        "created_by": {"type": "string"},
+        "file_id": {"type": "string"},
+    },
+
+    "required": ["postage", "filename", "created_by", "file_id"]
+}
diff --git a/tests/app/service/test_rest.py b/tests/app/service/test_rest.py
index 080d989d0..073d01a42 100644
--- a/tests/app/service/test_rest.py
+++ b/tests/app/service/test_rest.py
@@ -2297,6 +2297,23 @@ def test_create_pdf_letter(mocker, sample_service_full_permissions, client, fake
     assert json_resp == {'id': fake_uuid}
 
 
+def test_create_pdf_letter_validates_against_json_schema(sample_service_full_permissions, client):
+    response = client.post(
+        url_for('service.create_pdf_letter', service_id=sample_service_full_permissions.id),
+        data=json.dumps({}),
+        headers=[('Content-Type', 'application/json'), create_authorization_header()]
+    )
+    json_resp = json.loads(response.get_data(as_text=True))
+
+    assert response.status_code == 400
+    assert json_resp['errors'] == [
+        {'error': 'ValidationError', 'message': 'postage is a required property'},
+        {'error': 'ValidationError', 'message': 'filename is a required property'},
+        {'error': 'ValidationError', 'message': 'created_by is a required property'},
+        {'error': 'ValidationError', 'message': 'file_id is a required property'}
+    ]
+
+
 def test_get_notification_for_service_includes_template_redacted(admin_request, sample_notification):
     resp = admin_request.get(
         'service.get_notification_for_service',
diff --git a/tests/app/service/test_send_pdf_letter_notification.py b/tests/app/service/test_send_pdf_letter_notification.py
index e1fe8ef94..7b4c5bd49 100644
--- a/tests/app/service/test_send_pdf_letter_notification.py
+++ b/tests/app/service/test_send_pdf_letter_notification.py
@@ -51,26 +51,6 @@ def test_send_pdf_letter_notification_validates_created_by(
         send_pdf_letter_notification(sample_service_full_permissions.id, post_data)
 
 
-def test_send_pdf_letter_notification_validates_postage(
-    sample_service_full_permissions, fake_uuid, notify_user
-):
-    user = sample_service_full_permissions.users[0]
-    post_data = {'filename': 'valid.pdf', 'created_by': user.id, 'file_id': fake_uuid, 'postage': 'third'}
-
-    with pytest.raises(BadRequestError):
-        send_pdf_letter_notification(sample_service_full_permissions.id, post_data)
-
-
-def test_send_pdf_letter_notification_requires_postage(
-    sample_service_full_permissions, fake_uuid, notify_user
-):
-    user = sample_service_full_permissions.users[0]
-    post_data = {'filename': 'valid.pdf', 'created_by': user.id, 'file_id': fake_uuid}
-
-    with pytest.raises(BadRequestError):
-        send_pdf_letter_notification(sample_service_full_permissions.id, post_data)
-
-
 def test_send_pdf_letter_notification_raises_error_if_service_in_trial_mode(
     mocker,
     sample_service_full_permissions,