Senior Backend Engineer

Connexis Group; Greater London; On-site; GBP 90,000 - 130,000; Full time

Job summary

Connexis Group is seeking a senior Python developer to own the routing engine, billing infrastructure and webhook delivery. You will write high-performance code using Python, FastAPI and MongoDB, targeting sub-100ms p99 latency and robust idempotent processing.

You will shape the engineering bar for the next five hires and lead CRM connector platforms (HubSpot/Salesforce/Pipedrive).

Qualifications

• 6+ years building production Python services with async/await.
• Deep MongoDB experience including indexing, aggregation and transactions.
• Experience in billing or payments infrastructure.
• Care about correctness—money flows through this code.

Responsibilities

• Own ping-tree v2 (multi-buyer parallel routing).
• Lead the CRM connector platform (HubSpot/Salesforce/Pipedrive).
• Set the engineering bar for the next 5 hires.

Skills

Python

Async/await

MongoDB

Billing systems

Code correctness

Tools

FastAPI

Job description

Own the routing engine, billing infrastructure and webhook delivery. Python/FastAPI/MongoDB. We process every inbound lead through code you write — sub-100ms p99 latency, idempotent everything, audit-trail everything.

Who you are

• 6+ years building production Python services — async/await fluent
• Deep MongoDB experience including indexing, aggregation, transactions
• Have built billing or payments infra you're proud of
• Care about correctness — money flows through this code

What you'll own

• Own ping-tree v2 (multi-buyer parallel routing)
• Lead the CRM connector platform (HubSpot/Salesforce/Pipedrive)
• Set the engineering bar for the next 5 hires