I’ve build dozens of API endpoints for backend (and for an iOS app). Python's Django Framework works great for any modern JS Frameworks: Angular, React, Vue etc. Also I’ve created a web service that connects Django’s default DB with separate CRM system. That’s was made via SOAP requests and with WSDL service from our side. Also, I’ve optimized DB queries so managers can quickly download users reports. Most of the SQL queries was made in triggers and procedures to increase response time.