diff --git a/srv/channel-submission-service.js b/srv/channel-submission-service.js
index 32adf80de..552e92d67 100644
--- a/srv/channel-submission-service.js
+++ b/srv/channel-submission-service.js
@@ -4,6 +4,11 @@ export default class ChannelSubmissionService extends cds.ApplicationService {
   async init() {
     // Stamp server-controlled fields; never trust client-sent status / reviewer / submitter.
     this.before('CREATE', 'Submissions', (req) => {
+      // EDIT / REMOVE act on an existing channel — reject at submit time (400) instead of
+      // letting the row sit PENDING only to fail at approve. ADD carries no target.
+      if ((req.data.kind === 'EDIT' || req.data.kind === 'REMOVE') && !req.data.targetChannel_ID) {
+        return req.reject(400, `A target channel is required for ${req.data.kind} submissions.`, 'targetChannel_ID');
+      }
       req.data.submitterId = req.user.id;
       req.data.status = 'PENDING';
       req.data.reviewerId = null;
diff --git a/test/channel-submission-service.test.js b/test/channel-submission-service.test.js
index 025c634b3..074c63230 100644
--- a/test/channel-submission-service.test.js
+++ b/test/channel-submission-service.test.js
@@ -37,9 +37,23 @@ describe('ChannelSubmissionService', () => {
     expect(row.reviewNote).toBeNull();
   });
 
-  test('service is insert-only — READ is not allowed', async () => {
+  test('service is insert-only — READ is rejected 405 Method Not Allowed', async () => {
+    // CAP 10 answers a READ on an @insertonly entity with 405 (not a generic 4xx/5xx).
+    // Asserting the exact code proves the entity is insert-only rather than merely erroring.
     await expect(
       project.get('/channel-submissions/Submissions', authUser),
-    ).rejects.toMatchObject({ response: { status: expect.any(Number) } });
+    ).rejects.toMatchObject({ response: { status: 405 } });
+  });
+
+  test('EDIT without a target channel is rejected at submit time (400)', async () => {
+    await expect(
+      project.post('/channel-submissions/Submissions', { kind: 'EDIT', proposed: '{}' }, authUser),
+    ).rejects.toMatchObject({ response: { status: 400 } });
+  });
+
+  test('REMOVE without a target channel is rejected at submit time (400)', async () => {
+    await expect(
+      project.post('/channel-submissions/Submissions', { kind: 'REMOVE', proposed: '{}' }, authUser),
+    ).rejects.toMatchObject({ response: { status: 400 } });
   });
 });