Senior HubSpot Marketplace App Developer (Custom Channels + Workflow Extensions + Certification)

We are looking for a highly experienced HubSpot Marketplace App Developer to lead the end-to-end development, certification, and publishing of an official HubSpot App.

This is a full-scale Marketplace app build, not a basic integration. Only apply if you have proven experience shipping public HubSpot Marketplace apps — especially involving Custom Channels API and Workflow Extensions.

Project Overview

The goal is to design, develop, certify, and publish a public HubSpot Marketplace app that integrates a third-party messaging platform with HubSpot.

The app must support two integration levels:

Case 1: General Integration (Starter & Pro Users)

CRM Card (right sidebar) integration on Contact, Deal, Company, and Ticket records

Embedded iFrame chat interface per associated contact

Conversation-based display logic (phone number matching)

Real-time activity logging (inbound/outbound messages to timeline)

Two-way contact sync (name, phone, opt-in status)

Duplicate handling with one primary contact per phone number

Custom Workflow Action:

Send message template

Dynamic channel selection (real-time)

Dynamic template selection (real-time)

Placeholder handling

Native HubSpot reporting support:

Number of conversations

Templates used

Opt-ins collected

Unread conversations (per channel)

Message volume (inbound, outbound, AI agent)

Suggest the creation of new conversation if none exists

Case 2: Enterprise Integration (Service/Sales Hub Enterprise Only)

Full Custom Channels API integration

Native Inbox messaging support

Agents reply from HubSpot Inbox (messages sent via external API)

24-hour session handling logic:

Within 24h: free text allowed

Outside 24h: template selection required

UI must reflect the session status correctly

Critical Requirements

Must pass official HubSpot Marketplace certification

App must be publicly listed

Complete handover of source code and technical documentation

UX/UI must align seamlessly with HubSpot design standards

Robust error handling (including API outage handling)

All necessary technical steps required for certification are included in the scope

Required Expertise

You MUST have:

Proven experience publishing HubSpot Marketplace Apps

Deep knowledge of:

HubSpot Public Apps (OAuth, scopes, webhooks)

CRM Extensions (CRM Cards, iFrames)

Timeline Events API

Workflow Extensions API

Custom Channels API (required)

Conversations API

Experience handling Marketplace security review & certification process

Strong backend architecture experience (Node.js / TypeScript preferred)

Experience with scalable webhook and sync systems

This is senior-level work. Not suitable for junior or mid-level developers.

Deliverables

Fully functional HubSpot Marketplace app

Successful certification & approval

Public listing

Source code ownership transferred

Technical setup & maintenance documentation

Clean, well-commented codebase

Timeline

Target project start: Within 3 weeks

Completion target: Aggressive timeline — please propose a realistic delivery schedule based on experience.

When Applying, Please Include

Links to HubSpot Marketplace apps you have built

Specific experience with Custom Channels API

Experience with Workflow Extensions

Estimated timeline

Estimated fixed-price cost

Your proposed technical stack

Only apply if you have direct, production-level experience with HubSpot Marketplace apps.

We are looking for a senior, reliable partner who understands both the technical and certification complexity involved.