Senior Backend Engineer, Activation and Engagement Server (Growth)

Since we opened our doors in 2009, the world of commerce has evolved immensely, and so has Square. After enabling anyone to take payments and never miss a sale, we saw sellers stymied by disparate, outmoded products and tools that wouldn’t work together.

So we expanded into software and started building integrated, omnichannel solutions – to help sellers sell online, manage inventory, offer buy now, pay later functionality, book appointments, engage loyal buyers, and hire and pay staff. Across it all, we’ve embedded financial services tools at the point of sale, so merchants can access a business loan and manage their cash flow in one place. Afterpay furthers our goal to provide omnichannel tools that unlock meaningful value and growth, enabling sellers to capture the next generation shopper, increase order sizes, and compete at a larger scale.

Today, we are a partner to sellers of all sizes – large, enterprise-scale businesses with complex operations, sellers just starting, as well as merchants who began selling with Square and have grown larger over time. As our sellers grow, so do our solutions. There is a massive opportunity in front of us. We’re building a significant, meaningful, and lasting business, and we are helping sellers worldwide do the same.

The Role

The Activation and Engagement Server Team is a critical part of Square's Growth Product organization, with a mission to help more sellers use Square more. As part of the Growth Product team's strategy to Simplify, Automate, and Graduate seller experiences, we build and maintain the backend infrastructure that guides sellers from signup through their first payment and beyond into ongoing product engagement. We're directly contributing to Square's growth initiatives focused on increasing new volume and seller success. Our primary goal is to improve onboarding and engagement for Square sellers while maintaining the reliability, uptime, and scalability of critical backend services powering onboarding flows.

We're addressing significant opportunities in the seller onboarding journey by building robust, extensible APIs that enable web onboarding, point of sale, and international teams to deliver seamless activation experiences that convert and engage sellers at scale. Our work spans the entire seller journey from acquisition through activation and engagement, focusing on automating complex workflows and removing friction from critical seller moments.

We're looking for a Senior Backend Engineer to help us scale our platform, lead technical initiatives, and mentor the next generation of engineers as we accelerate Square's growth.

You Will

• Drive onboarding and engagement improvements by designing and building highly available backend services that power critical seller experiences, including setup guides, onboarding checklists, automated workflows, and engagement features


• Build scalable distributed systems to handle millions of seller interactions across web, mobile, and international platforms while maintaining high reliability SLOs


• Lead cross-team technical initiatives spanning multiple engineering organizations, coordinating architecture decisions to support Growth Product's strategy of simplification and automation


• Own the full feature lifecycle from requirements analysis through API design, implementation, testing, deployment, monitoring, and production support with direct impact on growth metrics


• Mentor and guide engineers across the team and broader organization through code reviews, technical discussions, and knowledge sharing


• Act as a technical leader for ambiguous, complex projects that require coordinating multiple stakeholders and driving to resolution


• Enable extensibility and automation by building systems that outside engineers can easily understand, diagnose, and extend, supporting Growth Product's principles of rapid iteration and empowerment

You Have

• 8+ years of hands-on experience building Java/Kotlin microservices and APIs at meaningful scale (exceptional candidates with less experience but proven track record will be considered)


• Strong expertise in distributed systems design and implementation, including experience with event-driven architectures, data consistency, workflow orchestration, and automation platforms


• Strong API design skills for both internal and external consumption (REST/gRPC) with focus on reliability, extensibility, and supporting high-conversion user experiences


• Production ownership experience including incident response, SLO management, and operational excellence in high-traffic environments


• Technical leadership track record on multi-person, cross-team projects with demonstrated ability to mentor and guide other engineers


• Growth mindset and bias toward action with accountability for business outcomes and passion for moving fast while maintaining quality


• Excellent communication and collaboration skills with proven ability to influence teams beyond your immediate scope and work effectively in a fast-paced, outcome-driven environment


• Experience with modern cloud infrastructure (AWS, Kubernetes, containerization) and CI/CD practices

Preferred Qualifications:

• Experience in growth engineering, conversion optimization, or funnel analysis


• Background with payments, onboarding/activation, user engagement, or fintech domains


• Experience building automation platforms or workflow orchestration systems


• Knowledge of A/B testing frameworks and experimentation platforms


• Background with high-scale consumer or B2B SaaS products focused on user activation and retention

Technologies We Use and Teach

• Languages: Java(primary), Kotlin


• APIs & Communication: gRPC, REST, Protocol Buffers


• Frameworks: Guice, Hibernate


• Experimentation: Optimizely, LaunchDarkly.


• Testing: JUnit, Mockito, integration testing frameworks

We’re working to build a more inclusive economy where our customers have equal access to opportunity, and we strive to live by these same values in building our workplace. Block is an equal opportunity employer evaluating all employees and job applicants without regard to identity or any legally protected class. We will consider qualified applicants with arrest or conviction records for employment in accordance with state and local laws and "fair chance" ordinances.

We believe in being fair, and are committed to an inclusive interview experience, including providing reasonable accommodations to disabled applicants throughout the recruitment process. We encourage applicants to share any needed accommodations with their recruiter, who will treat these requests as confidentially as possible. Want to learn more about what we’re doing to build a workplace that is fair and square? Check out our I+D page .

While there is no specific deadline to apply for this role, U.S. roles are typically open for an average of 55 days before being filled by a successful candidate. Please refer to the date listed at the top of this job page for when this role was first posted.