Finance Operator in Residence (Order-to-cash)
What you need
- 2-3 yrs order-to-cash/AR/credit control experience
- Enterprise-scale finance operations experience
- Proficient with customer ledgers, payment allocation, reconciliation, ERP
- Can resolve complex cases, explain reasoning clearly
- Confident using AI tools, shaping agent behavior
What you'll do
- Serve as order-to-cash SME for customer operations
- Review/approve AI agent actions, handle exceptions
- Collaborate with customer finance teams on payment blockers
- Develop procedures, improve agent behavior with engineering
- Configure agents per customer policies
AI Transformation for Enterprise Finance
Rex builds AI agents for enterprise finance, starting with order to cash. Our customers delegate a process to us, and we run it with agents while finance experts oversee the work. Our agents operate across email, ERPs and customer portals to resolve payment blockers and help businesses get paid.
We’re building agents that can take responsibility for complex financial workflows: reason over messy data, handle exceptions and improve through feedback from finance experts. The challenge is earning the trust to act autonomously in operations that affect real money.
Who we are
Rex was founded in 2026 by Merlin Kafka (CEO) and Lewis Blackwood (CTO).
Merlin previously served as CPO at Sequence (a16z) and PM at Tessian (Sequoia), and studied industrial engineering at Cambridge. Lewis previously led engineering at Sequence, joined GoCardless early and founded a startup backed by GFC. He studied economics at Cambridge.
Our team brings years of experience building AI and finance products and working with hundreds of finance teams. We know this domain inside-out.
Rex is global from day one and operates across San Francisco and London.
What you’ll do
You’ll be the team’s subject matter expert on order to cash and help run customer operations alongside Rex’s agents. You’ll bring practical knowledge of billing, collections, cash application and reconciliation into how we build the product and configure agents for each customer.
Day to day, you’ll review and approve agent actions, handle exceptions and resolve cases that need human judgment. You’ll work closely with customer finance teams to understand their policies, investigate payment blockers and keep the work moving.
You’ll turn what you learn into clearer procedures and better agent behaviour, working directly with engineering.
You’ll fit if you
- Have around 2-3 years of hands-on experience in order to cash, AR or credit control, ideally at enterprise scale.
- Are comfortable with customer ledgers, payment allocation, reconciliation and ERP systems.
- Can work through complex cases and explain your reasoning clearly to customers and engineers.
- Use AI tools confidently and want to help shape how agents run finance operations.
This role is an ideal fit for an AI-native operator who spent the last few years working in order to cash or AR at enterprise scale and now wants to put their domain knowledge to work.
This role is full-time in-person in London.
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About Rex
Rex is an AI-native service for order to cash. We replace people-heavy operations with AI agents that continuously manage invoices, customers and exceptions. Order to cash is a $60B outsourced function because the work is too messy for traditional automation. Every customer has different context, exceptions do not follow clean rules, and the next step is often buried in emails, portals, handoffs, or someone’s memory. Rex agents run continuously in the background and resolve work to SLA standards so cash keeps moving. We're live with pre-IPO tech companies, managing >$500m in receivables from F100 companies, cutting manual follow-up cycles from weeks to hours. We founded Rex after spending four years building Sequence, an a16z-backed finance ops platform, from zero to Series A — where we saw firsthand that at-scale, O2C still runs on manual labour. Rex is the #1 winner of the Vercel AI Accelerator out of 2,500 teams, selected by Guillermo Rauch and leaders from OpenAI, Anthropic, Browserbase and more.
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