Job Title: Senior Base24 / Base24 Classic DeveloperLocation: BrazilClient: FiservBudget: $4,500 USD as CONTRACTOR (No benefits)Duration: Long-termEmployment Type: Full-TimeAbout the RoleWe are seeking an experienced Base24 / Base24 Classic Developer to support payment switch development, enhancement, and operational stability within a high-volume card transaction environment. The ideal candidate has hands-on experience working with Tandem/HP NonStop systems, Base24 modules, issuer/acquirer interfaces, and ATM/POS transaction processing flows.This role requires strong technical depth in transaction message processing (ISO 8583), ATM/POS terminal driving, and tuning systems for high availability and performance. The developer will work closely with cross-functional teams including Product, Application Support, Network Security, and Environment Infrastructure.Key Responsibilities- Develop, configure, enhance, and support Base24 / Base24 Classic applications on HP NonStop (Tandem) platform.- Maintain and modify ATM/POS transaction switch modules, authorization, settlement, and device handler components.- Monitor and troubleshoot end-to-end transaction flows including issuer/acquirer interfaces.- Analyze and resolve production issues with strong ownership of incident/problem resolution.- Implement code enhancements, patches, and release changes in alignment with governance and compliance standards.- Design and execute system integration testing, regression testing, and certification testing with network partners (Visa/Mastercard).- Work with cross-functional teams to support performance tuning, batch processing, and environment stability.- Ensure secure, compliant, and resilient handling of financial transaction data.- Prepare and maintain detailed technical documentation, release notes, and operational runbooks.Required Skills & Experience- 5+ years hands-on experience with Base24 or Base24 Classic.- Strong technical expertise in:- HP NonStop / Tandem (Guardian, OSS)- Pathway, TAL, COBOL, SCOBOL, C, TACL, DDL, SQL/Enscribe- ATM and POS network protocols- ISO 8583 message formats- Experience supporting high-availability, transaction-intensive payment switching platforms.- Hands-on experience in debugging, log analysis, and performance tuning in a production environment.- Knowledge of Visa/Mastercard authorization and clearing, card bin tables, key exchange, PIN translation.- Experience in incident management, change control, and release management.Good to Have- Exposure to Base24-eps migration or development.- Experience working with Fiserv, First Data, TSYS, ACI Postilion, or Opus environments.- Knowledge of EMV, HSM (Thales / SafeNet), cryptographic key management.- Experience with Jira, Confluence, Git, and CI/CD toolchains.Education- Bachelor’s degree in Computer Science, Engineering, Information Systems, or related field (or equivalent work experience).