angular error 4 HPE_INVALID_CONSTANT

I'm trying to download via api rest, my application works fine with api, but when I try to request files, PDF for example it returns the following error:

 [HPM] Error occurred while trying to proxy request /api/v1/invoices/5aa030e1e1bfd700105eaee5 from localhost:4200 to 145.239.197.46 (HPE_INVALID_CONSTANT) (https://nodejs.org/api/errors.html#errors_common_system_errors)

My proxy.conf.json file is configured as follows:

    {
      "/api": {
        "target": {
          "host": "145.239.197.46",
          "protocol": "http:",
          "port": 8000
        },
        "secure": false,
        "changeOrigin": true,
        "logLevel": "info"
      }
    }

and my configuration .lang-cli-json is with the script as follows:

"scripts": {
    "ng": "ng",
    "conventional-changelog": "conventional-changelog",
    "start": "ng serve --proxy-config proxy.conf.json --host 0.0.0.0 --port 4200",
    "build": "ng build",
    "build:prod": "npm run build -- --prod --aot",
    "test": "ng test -sr",
    "test:coverage": "rimraf coverage && npm run test -- -cc",
    "lint": "ng lint --type-check",
    "lint:fix": "ng lint --fix",
    "lint:styles": "stylelint ./src/**/*.scss",
    "lint:ci": "npm run lint && npm run lint:styles",
    "pree2e": "webdriver-manager update --standalone false --gecko false",
    "e2e": "ng e2e",
    "docs": "compodoc -p src/tsconfig.app.json -d docs",
    "docs:serve": "compodoc -p src/tsconfig.app.json -d docs -s",
    "prepush": "npm run lint:ci",
    "release:changelog": "npm run conventional-changelog -- -p angular -i CHANGELOG.md -s"
  },

I'm using angular 2/4 Any suggestion of what can cause this? Thank you.