Readymade WhatsApp Clone or Custom Build — Messaging App (Mobile + Desktop + Browser)

We're looking for a developer or team to help us acquire and customize an existing WhatsApp-style chat application to match our specific requirements — rather than building entirely from scratch. Preferred approach: We're open to purchasing an existing app/source code (e.g., from marketplaces like CodeCanyon) that already covers most core chat/calling functionality, and having a developer customize it to add our specific requirements below. If no suitable existing solution can be adapted, we're also open to a fully custom build — please indicate which approach you'd recommend and why. What we need, either way: 1.⁠ ⁠Desktop & Mobile Connection Users start their computer, open the mobile app, and scan a QR/barcode to connect the desktop app — similar to WhatsApp Web Android, iOS, and desktop versions required 2.⁠ ⁠User Registration & Accounts Sign-up via email address, with First Name and Last Name Accounts created under our brand System auto-generates a unique username and password Other users only see full name; users are searchable by unique username once shared 3.⁠ ⁠Key-Based Access System App launch shows "Enter Key" or "Get Key" Only Admin can create, issue, and manage access keys Please advise on best architecture for multi-device key management 4.⁠ ⁠Messaging Real-time text messaging and file sharing Only Admin can delete messages/conversations — not regular users 5.⁠ ⁠Calling App-to-app voice/video calling Admin controls who can call whom — some users can call each other, others cannot unless granted permission 6.⁠ ⁠Groups Only Admin can create groups and add/remove members 7.⁠ ⁠Recording & Monitoring Conversation recording with noise cancellation Automatic screenshot capture at set intervals Secure, access-controlled storage for recordings and screenshots 8.⁠ ⁠Notifications Push notifications and real-time updates 9.⁠ ⁠Deployment No public App Store/Play Store submission — private/enterprise distribution only (Apple Business/Enterprise Program for iOS, direct APK/private distribution for Android) SDK/source code access required so we retain full modification rights How to apply — please include: Whether you'd recommend buying-and-customizing an existing app or building custom, and why If recommending an existing app: which one, and a link/demo if possible Your experience with similar projects (messaging apps, admin-permission systems, key-based access, multi-device apps) Recommended technology stack Fixed price and realistic timeline (please break down by phase if possible) Any questions on system design — particularly around key management, QR pairing architecture, or the recording/screenshot implementation Budget: Open to proposals — please quote based on the scope above. Timeline: Flexible, but please provide a realistic estimate. Contract: Freelance, with NDA and IP protection agreement.