Edit Backend for Crypto Transactions

I’m looking for a seasoned full-stack developer with proven blockchain expertise to jump into my existing codebase and fix the back-end layer that powers our cryptocurrency transactions. The front-end is stable; the problems surface server-side where transactions are built, signed, and broadcast... (Budget: $30 - $250 USD, Jobs: API Development, Blockchain, Cryptocurrency, Full Stack Development, Java, MySQL, PHP, Software Architecture)