About the role

Role Overview

Staff Software Engineer (Backend) for the core platform team at Flex/Sundayy. You’ll shape the long-term architecture of backend services while staying hands-on with coding and end-to-end system delivery in a small, collaborative, remote-first environment.

Responsibilities

Design, implement, and maintain the company’s Finance service and internal tooling (financial reporting, reconciliation, audit processes)
Develop and enhance APIs to support large monetary transactions across banking partners via payment rails (e.g., ACH)
Scale core platform infrastructure for business growth while maintaining high performance and reliability
Improve operational efficiency through automation, tooling, observability, and system design evolution
Collaborate with product, design, analytics, and finance (and engineering) to launch and enhance financial features
Mentor and guide engineers, raising technical standards and best practices
Ensure systems are secure, compliant, and resilient against failures and security threats
Participate in code reviews, architecture discussions, and technical decision-making

Requirements

6+ years of software development experience
Proven technical leadership experience guiding complex projects/teams
Proficiency in Java, Python, Go (Golang), or TypeScript/Node.js
Strong database skills with relational SQL and NoSQL (e.g., MySQL, PostgreSQL, DynamoDB)
Experience designing and building fault-tolerant, scalable distributed systems
Hands-on experience with AWS services including EKS, Lambda, API Gateway, VPN, RDS (and more)
Familiarity with Infrastructure as Code tools such as AWS CDK, AWS CLI, or Terraform
Strong communication skills with the ability to explain technical concepts to non-technical stakeholders
Experience with finance reporting, reconciliation, and data mining
Proactive approach to automation/tooling and strong problem-solving

Nice-to-Haves

Not explicitly listed beyond the finance/analytics and distributed-systems depth required above.

About Sundayy

The posting describes Sundayy/Flex as a growth-stage FinTech company headquartered in New York City. The company focuses on revolutionizing the rent payment experience by helping renters pay flexibly, improving control and convenience around a major recurring expense. It operates in the consumer financial services space and builds technology that supports partner integrations and core financial operations.

Software Engineer, Backend

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