SENIOR .NET DEVELOPER — INTEGRATIONS & APIs

SENIOR .NET DEVELOPER — INTEGRATIONS & APIs Nearshore📍Remote | Contract, full-time (40 hrs/week) | Colombia
Own the places where money actually moves
We're looking for a Senior .NET Developer to own the boundary between our platform and everyone else's. Our system talks to a card processor, an ACH gateway, QuickBooks, Twilio, Mailchimp, and Slack — mostly over REST — and those integrations are getting rebuilt as part of a larger modernization. This is where money leaves and arrives, so precision here isn't optional, it's the job.
If you like the kind of problem where "it worked" isn't good enough until you've also proven it can't double-charge anyone — this seat is for you.
What you'll be doing
Reimplementing existing third-party integrations against modern clients — the card processor, ACH gateway, QuickBooks, Twilio, Mailchimp, and Slack.
Handling the unglamorous parts properly: retries, idempotency, timeouts, and partial failures, so a hiccup on someone else's end never turns into a mistake on ours.
Reconciling what a vendor says happened against what we actually recorded — because those two stories don't always agree, and figuring out why is half the work.
Building internal APIs for the modernized system.
Carrying a share of legacy corrective maintenance on the existing integrations.
What you'll need
Strong C# and ASP.NET 4.7, plus .NET 8 and .NET 10
Real, hands-on REST integration experience against third-party services you don't control
A genuine understanding of idempotency and retry semantics — double-charging someone is the failure we're designing against
Comfort reading vendor documentation that is, itself, sometimes wrong
Professional English, spoken and written
Minimum 4 hours of overlap with US Central time
Availability for full-time work, 40 hours/week
Nice to have
Experience integrating payment gateways or accounting systems specifically
Web hook handling experience
Experience reconciling financial records across systems
One more thing we look for in every seat
Comfort working with AI-assisted development tools — not just using them, but directing an agent well on real work and reviewing what it hands back before it ships. If you already think this way, you'll feel at home here.
Good to know
This seat works in non-production environments only, with synthetic or sanitized data. You'll write the fixes for legacy issues, but deployment and production data access sit outside this role.

Work arrangement
Yes