API integration developer for billing, webhooks and third-party data
I connect systems that were not built to talk to each other: billing, auth, e-signature, email, CRMs and third-party data APIs. At Axiom Realty Solutions I integrated a dozen external REST APIs with retry, backoff and fault-tolerant fallbacks, and OnOffDeals runs live Stripe billing on a webhook-driven state machine I designed.
- A dozen REST APIs integrated at Axiom
- Webhook-driven Stripe billing
- Referrals mirrored into GoHighLevel
Integrations I have shipped
Each of these is wired into a live product or business process. The work is rarely the first successful API call. It is mapping the other system’s data onto yours, handling its errors and edge cases, and making sure a failure shows up somewhere a person will see it rather than disappearing into a log nobody reads.
- Stripe: subscriptions, trials, coupons, usage metering and webhooks
- Clerk + JWT auth with role-based access
- DocuSign and PDF/Excel exports in OnOffDeals
- Resend transactional email and Cloudflare R2 media storage
- GoHighLevel webhooks, Google Sheets and Workspace APIs
- Zillow API, Apify and the Anthropic Claude API
Retries, backoff and fallbacks
External APIs time out, rate-limit and change their response shapes. At Axiom Realty Solutions the dozen APIs I integrated sit behind retry with backoff and fault-tolerant fallbacks, so one slow provider does not stall the whole pipeline. At Podiam AI I replaced a local LaTeX dependency with a serverless LaTeX-to-PDF pipeline that falls back across multiple APIs. In OnOffDeals, Stripe events drive a state machine, so subscription status follows what Stripe reports.
Keeping third-party API costs under control
Paid data APIs can quietly eat a product’s margin. In OnOffDeals I built versioned market caching and batched prefetching so third-party property-data costs stay viable under rate limits. On the revenue side, per-plan usage metering with overage in Stripe ties heavy usage to the plans that pay for it. I look at caching and batching before reaching for a bigger API tier.
CRM and webhook plumbing
For PowerSmith Energy the referral pipeline is mirrored into GoHighLevel via webhooks, and every referral carries both the partner and the rep, so attribution survives the hand-off between systems. In n8n I built an event API that validates an ID, checks availability and returns clean data to a GoHighLevel funnel with 400 and 404 error handling, plus a Slack task bot driven by Slack Events webhooks.
Rates from $20/hour
Hourly for open-ended work, fixed price for defined projects. The first call is free and there's no obligation.
Frequently asked questions
Do you write custom code or use n8n, Make and Zapier for integrations?
Both. n8n, Make and Zapier are quick to build and easy for a team to inspect, and I have shipped 50+ automation workflows with them. When an integration needs state, volume, retries or careful money handling, I write it in Python or Node.js instead.
Can you integrate an API with poor or missing documentation?
Yes. I capture real requests and responses, write a small client around them and test the edge cases before wiring it into your product. Undocumented systems are familiar ground: I often work in inherited codebases with no documentation at all.
How do you deal with API rate limits?
Caching first, then batching, then backoff. In OnOffDeals, versioned caching and batched prefetching keep a rate-limited data API usable and affordable, and retries with backoff handle the limits that remain.
What does an API integration project cost?
Rates start from $20/hour. A single well-defined integration, such as connecting Stripe billing or a CRM webhook, can usually be quoted at a fixed price after a free 30-minute call.