cvcallahan.com Integration Engineering reach@cvcallahan.com

We design, build and operate the third-party API connections that B2B software and the businesses running it depend on — payments, CRM, ERP, billing, identity.

Category Integration engineering. B2B only.
Buyers Software vendors shipping integrations to their own customers · operating companies whose stack doesn’t reconcile
Model Bespoke. Scoped in conversation.
Not sold Staff augmentation · general web development · marketing
Contact reach@cvcallahan.com

Product

5 practices
  1. Full AMS Launch E2e development from proposal, architecture, strategy, and launch
  2. E-Commerce Platform Launch Driving growth through improved UX along payment pathways
  3. Integration & Technical Strategy Assessing APIs, vendors, and integration paths to make informed decisions about cost, complexity, reliability, and scalability.
  4. Application Workflows & Automation Reducing manual work through reliable automation across scheduled, transactional, and operational workflows.
  5. Product Architecture & Data Modeling Designing scalable foundations for products, integrations, and the data that connects them.

Build

6 disciplines
  1. Third-party integrations Payments, CRM, ERP, accounting, billing, LMS, comms. REST, GraphQL, webhooks, file and SFTP feeds.
  2. Custom API design Versioning, auth, pagination, idempotency, error contracts. Partner and public surfaces.
  3. Sync & middleware services Field mapping, retries, dead-letter handling, reconciliation, replay.
  4. Vendor & gateway migration Token vaults, dual-write cutovers, reconciliation ledgers, rollback paths. Payment gateways, CRMs, billing systems.
  5. Data migration & backfill Idempotent and resumable movement. Identity on stable business keys, never on primary keys. Dry runs, row-level reconciliation.
  6. Embedded integration catalogs Customer-facing connector catalogs inside your product. Per-tenant credentials, scoped access, extensible connector patterns.

Against

67 of 67 platforms · 8 categories
Clear
Payments
CRM & Marketing
Email & Comms
Accounting & ERP
Identity & Auth
Association & Community
Commerce & CMS
Data & Infra

Recent Work

5 selected
  • 2026 Payment gateway replacement Membership / association software Vendor & gateway migration FlaskPostgreSQLCeleryCardPointe
  • 2026 Renewal billing reconciliation Subscription billing Sync & middleware FlaskPostgreSQLCelery
  • 2025 Association CRM (full replacement) Association management Replatform & legacy rewrite FlaskPostgreSQLCelery
  • 2025 Accounting sync Finance operations Third-party integration CeleryQuickBooks Online
  • 2025 Multi-service OAuth2 identity provider Platform / identity Custom API design AuthlibOAuth2 / OIDC