The correct endpoint is http://prisma:4466/lpwanserver/dev.
prisma/prisma.yml should read:
endpoint: ${env:prisma_url}
This causes causes the generated DB client to attempt to connect to process.env.prisma_url. You can check if the client was generated correctly by viewing app/generated/prisma-client/index.js. Towards the bottom of the file, you should see process.env.prisma_url. The development/docker-compose file sets the config file to development/config.json. In that file, the prisma_url is set to http://prisma:4466/lpwanserver/dev. All config variables can be overwritten with environment variables, but in case prisma_url comes from a config file and not an environment variable, the module app/config/index.js writes the value of config.prisma_url to process.env.prisma_url so that it can be used by the DB client.