diff --git a/src/milestones/milestones.service.spec.ts b/src/milestones/milestones.service.spec.ts
index 492c562..16e362e 100644
--- a/src/milestones/milestones.service.spec.ts
+++ b/src/milestones/milestones.service.spec.ts
@@ -8,15 +8,22 @@ import { AssetType, MilestoneStatus } from '../common/enums';
 describe('MilestonesService', () => {
   let service: MilestonesService;
   let milestoneRepo: { findOne: jest.Mock; save: jest.Mock };
-  let escrowService: { fund: jest.Mock };
+  let issueRepo: { findOne: jest.Mock; save: jest.Mock; update: jest.Mock };
+  let escrowService: { fund: jest.Mock; releasePartial: jest.Mock };
 
   beforeEach(async () => {
     milestoneRepo = {
       findOne: jest.fn(),
       save: jest.fn((m: Partial<Milestone>) => Promise.resolve(m)),
     };
+    issueRepo = {
+      findOne: jest.fn(),
+      save: jest.fn((i: Partial<Issue>) => Promise.resolve(i)),
+      update: jest.fn().mockResolvedValue({ affected: 1 }),
+    };
     escrowService = {
       fund: jest.fn().mockResolvedValue({ id: 'escrow-1', status: 'locked' }),
+      releasePartial: jest.fn().mockResolvedValue({ id: 'payment-1', amount: '100' }),
     };
 
     const module: TestingModule = await Test.createTestingModule({
@@ -25,7 +32,7 @@ describe('MilestonesService', () => {
         { provide: getRepositoryToken(Milestone), useValue: milestoneRepo },
         {
           provide: getRepositoryToken(Issue),
-          useValue: { findOne: jest.fn() },
+          useValue: issueRepo,
         },
         { provide: EscrowService, useValue: escrowService },
       ],
@@ -97,4 +104,96 @@ describe('MilestonesService', () => {
       );
     });
   });
+
+  describe('addIssue', () => {
+    it('successfully attaches an issue when repositoryId matches', async () => {
+      milestoneRepo.findOne.mockResolvedValue({
+        id: 'm-1',
+        repositoryId: 'repo-a',
+        issues: [],
+      });
+      issueRepo.findOne.mockResolvedValue({
+        id: 'issue-1',
+        repositoryId: 'repo-a',
+        milestoneId: null,
+      });
+
+      const result = await service.addIssue('m-1', 'issue-1');
+
+      expect(result.milestoneId).toBe('m-1');
+      expect(issueRepo.save).toHaveBeenCalledWith(
+        expect.objectContaining({
+          id: 'issue-1',
+          milestoneId: 'm-1',
+        }),
+      );
+    });
+
+    it('rejects attaching an issue from a different repository with clear mismatch details', async () => {
+      milestoneRepo.findOne.mockResolvedValue({
+        id: 'm-1',
+        repositoryId: 'repo-a',
+        issues: [],
+      });
+      issueRepo.findOne.mockResolvedValue({
+        id: 'issue-2',
+        repositoryId: 'repo-b',
+        milestoneId: null,
+      });
+
+      await expect(service.addIssue('m-1', 'issue-2')).rejects.toThrow(
+        'Issue issue-2 (repository: repo-b) does not belong to Milestone m-1 repository (repo-a)',
+      );
+      expect(issueRepo.save).not.toHaveBeenCalled();
+    });
+
+    it('throws NotFoundException when issue does not exist', async () => {
+      milestoneRepo.findOne.mockResolvedValue({
+        id: 'm-1',
+        repositoryId: 'repo-a',
+        issues: [],
+      });
+      issueRepo.findOne.mockResolvedValue(null);
+
+      await expect(service.addIssue('m-1', 'issue-missing')).rejects.toThrow(
+        'Issue issue-missing not found',
+      );
+    });
+  });
+
+  describe('resolveIssue', () => {
+    it('computes proportional share and resolves issue successfully', async () => {
+      milestoneRepo.findOne.mockResolvedValue({
+        id: 'm-1',
+        repositoryId: 'repo-a',
+        status: MilestoneStatus.FUNDED,
+        escrowId: 'escrow-1',
+        budget: '200.0000000',
+        distributed: '0.0000000',
+        issues: [
+          { id: 'issue-1', state: 'open', repositoryId: 'repo-a' },
+          { id: 'issue-2', state: 'open', repositoryId: 'repo-a' },
+        ],
+      });
+
+      const payment = await service.resolveIssue(
+        'm-1',
+        'issue-1',
+        'GRECIPIENT',
+        'user-1',
+      );
+
+      expect(escrowService.releasePartial).toHaveBeenCalledWith(
+        'escrow-1',
+        '100.0000000',
+        'GRECIPIENT',
+        'user-1',
+      );
+      expect(issueRepo.update).toHaveBeenCalledWith('issue-1', {
+        state: 'closed',
+        closedAt: expect.any(Date),
+      });
+      expect(payment).toEqual({ id: 'payment-1', amount: '100' });
+    });
+  });
 });
diff --git a/src/milestones/milestones.service.ts b/src/milestones/milestones.service.ts
index 43bb7fb..89e8064 100644
--- a/src/milestones/milestones.service.ts
+++ b/src/milestones/milestones.service.ts
@@ -70,6 +70,13 @@ export class MilestonesService {
     const milestone = await this.findOne(milestoneId);
     const issue = await this.issueRepo.findOne({ where: { id: issueId } });
     if (!issue) throw new NotFoundException(`Issue ${issueId} not found`);
+
+    if (issue.repositoryId !== milestone.repositoryId) {
+      throw new BadRequestException(
+        `Issue ${issueId} (repository: ${issue.repositoryId}) does not belong to Milestone ${milestoneId} repository (${milestone.repositoryId})`,
+      );
+    }
+
     issue.milestoneId = milestone.id;
     return this.issueRepo.save(issue);
   }