Error: Can not find the module 'express' when transmitting the node application to Heroku.

A complete beginner creating node applications and deploying on Heroku I've built my application with React.js (create-react-app), Node and Express.

Everything works well locally, but I get the error below when I push on Heroku.

2019-02-26T05: 25: 34.482091 + 00: 00 app[web.1]:
2019-02-26T05: 25: 34.578028 + 00: 00 app[web.1]: internal / modules / cjs / loader.js: 583
2019-02-26T05: 25: 34.578031 + 00: 00 app[web.1]: throw err;
2019-02-26T05: 25: 34.578033 + 00: 00 app[web.1]: ^
2019-02-26T05: 25: 34.578034 + 00: 00 app[web.1]:
2019-02-26T05: 25: 34.578036 + 00: 00 app[web.1]: Error: Can not find module 'express'
2019-02-26T05: 25: 34.578049 + 00: 00 app[web.1]: at Function.Module._resolveFilename (internal / modules / cjs / loader.js: 581: 15)
2019-02-26T05: 25: 34.578051 + 00: 00 app[web.1]: at Function.Module._load (internal / modules / cjs / loader.js: 507: 25)
2019-02-26T05: 25: 34.578053 + 00: 00 app[web.1]: in Module.require (internal / modules / cjs / loader.js: 637: 17)
2019-02-26T05: 25: 34.578054 + 00: 00 app[web.1]: at require (internal / modules / cjs / helpers.js: 22: 18)
2019-02-26T05: 25: 34.578056 + 00: 00 app[web.1]: to the object. (/App/app.js:1:79)
2019-02-26T05: 25: 34.578057 + 00: 00 app[web.1]: in Module._compile (internal / modules / cjs / loader.js: 689: 30)
2019-02-26T05: 25: 34.578059 + 00: 00 app[web.1]: at Object.Module._extensions..js (internal / modules / cjs / loader.js: 700: 10)
2019-02-26T05: 25: 34.578060 + 00: 00 app[web.1]: in Module.load (internal / modules / cjs / loader.js: 599: 32)
2019-02-26T05: 25: 34.578062 + 00: 00 app[web.1]: on tryModuleLoad (internal / modules / cjs / loader.js: 538: 12)
2019-02-26T05: 25: 34.578064 + 00: 00 app[web.1]: at Function.Module._load (internal / modules / cjs / loader.js: 530: 3)
2019-02-26T05: 25: 34.583038 + 00: 00 app[web.1]: npm ERR! ELIFECYCLE code
2019-02-26T05: 25: 34.583529 + 00: 00 app[web.1]: npm ERR! errno 1
2019-02-26T05: 25: 34.584697 + 00: 00 app[web.1]: npm ERR! zenform2@1.0.0 start: `node. / bin / www`
2019-02-26T05: 25: 34.584932 + 00: 00 app[web.1]: npm ERR! Release status 1
2019-02-26T05: 25: 34.585268 + 00: 00 app[web.1]: npm ERR!
2019-02-26T05: 25: 34.585524 + 00: 00 app[web.1]: npm ERR! Failed zenform2@1.0.0 startup script.
2019-02-26T05: 25: 34.585778 + 00: 00 app[web.1]: npm ERR! This is probably not a problem with NPM. There is probably an additional logging output above.
2019-02-26T05: 25: 34.590694 + 00: 00 app[web.1]:
2019-02-26T05: 25: 34.590929 + 00: 00 app[web.1]: npm ERR! A complete diary of this run can be found in:
2019-02-26T05: 25: 34.591075 + 00: 00 app[web.1]: npm ERR! /app/.npm/_logs/2019-02-26T05_25_34_587Z-debug.log
2019-02-26T05: 25: 34.657660 + 00: 00 heroku[web.1]: Process left with status 1
2019-02-26T05: 25: 41.203272 + 00: 00 heroku[router]: at = error code = H10 desc = "application blocked" method = GET path = "/" host = www.zenform.co request_id = 7ae2bd9a-1fe6-405d-8507-b65575e34254 fwd = "76.102.21.229" dyno = connect = service = status = 503 bytes = protocol = http
2019-02-26T05: 32: 12.000000 + 00: 00 application[api]: Construction started by the user zenform.co@gmail.com
2019-02-26T05: 34: 04.264186 + 00: 00 heroku[web.1]: The state has gone from stuck to start
2019-02-26T05: 34: 04.060723 + 00: 00 app[api]: Deploy ec860d98 by the user zenform.co@gmail.com
2019-02-26T05: 34: 04.060723 + 00: 00 app[api]: Version v73 created by the user zenform.co@gmail.com
2019-02-26T05: 34: 04.000000 + 00: 00 application[api]: Successful construction
2019-02-26T05: 34: 19.208996 + 00: 00 heroku[web.1]: Startup Process with the `npm start` Command
2019-02-26T05: 34: 22.706524 + 00: 00 heroku[web.1]: State changed from start to crash
2019-02-26T05: 34: 22.737586 + 00: 00 heroku[web.1]: The state has gone from stuck to start
2019-02-26T05: 34: 22.557721 + 00: 00 app[web.1]: internal / modules / cjs / loader.js: 583
2019-02-26T05: 34: 22.557738 + 00: 00 app[web.1]: throw err;
2019-02-26T05: 34: 22.557739 + 00: 00 app[web.1]: ^
2019-02-26T05: 34: 22.557740 + 00: 00 app[web.1]:
2019-02-26T05: 34: 22.557742 + 00: 00 app[web.1]: Error: Can not find module 'express'
2019-02-26T05: 34: 22.557744 + 00: 00 app[web.1]: at Function.Module._resolveFilename (internal / modules / cjs / loader.js: 581: 15)
2019-02-26T05: 34: 22.557745 + 00: 00 app[web.1]: at Function.Module._load (internal / modules / cjs / loader.js: 507: 25)
2019-02-26T05: 34: 22.557747 + 00: 00 app[web.1]: in Module.require (internal / modules / cjs / loader.js: 637: 17)
2019-02-26T05: 34: 22.557748 + 00: 00 app[web.1]: at require (internal / modules / cjs / helpers.js: 22: 18)
2019-02-26T05: 34: 22.557750 + 00: 00 app[web.1]: to the object. (/App/app.js:1:79)
2019-02-26T05: 34: 22.557752 + 00: 00 app[web.1]: in Module._compile (internal / modules / cjs / loader.js: 689: 30)
2019-02-26T05: 34: 22.557753 + 00: 00 app[web.1]: at Object.Module._extensions..js (internal / modules / cjs / loader.js: 700: 10)
2019-02-26T05: 34: 22.557755 + 00: 00 app[web.1]: in Module.load (internal / modules / cjs / loader.js: 599: 32)
2019-02-26T05: 34: 22.557757 + 00: 00 app[web.1]: on tryModuleLoad (internal / modules / cjs / loader.js: 538: 12)
2019-02-26T05: 34: 22.557758 + 00: 00 app[web.1]: at Function.Module._load (internal / modules / cjs / loader.js: 530: 3)
2019-02-26T05: 34: 22.568138 + 00: 00 app[web.1]: npm ERR! ELIFECYCLE code
2019-02-26T05: 34: 22.568712 + 00: 00 app[web.1]: npm ERR! errno 1
2019-02-26T05: 34: 22.570298 + 00: 00 app[web.1]: npm ERR! zenform2@1.0.0 start: `node. / bin / www`
2019-02-26T05: 34: 22.570546 + 00: 00 app[web.1]: npm ERR! Release status 1
2019-02-26T05: 34: 22.570909 + 00: 00 app[web.1]: npm ERR!
2019-02-26T05: 34: 22.571155 + 00: 00 app[web.1]: npm ERR! Failed zenform2@1.0.0 startup script.
2019-02-26T05: 34: 22.571389 + 00: 00 app[web.1]: npm ERR! This is probably not a problem with NPM. There is probably an additional logging output above.
2019-02-26T05: 34: 22.594258 + 00: 00 app[web.1]:
2019-02-26T05: 34: 22.603782 + 00: 00 app[web.1]: npm ERR! A complete diary of this run can be found in:
2019-02-26T05: 34: 22.603786 + 00: 00 app[web.1]: npm ERR! /app/.npm/_logs/2019-02-26T05_34_22_573Z-debug.log
2019-02-26T05: 34: 22.294657 + 00: 00 app[web.1]:
2019-02-26T05: 34: 22.294678 + 00: 00 app[web.1]:> zenform2@1.0.0 start / app
2019-02-26T05: 34: 22.294680 + 00: 00 app[web.1]:> node ./bin/www
2019-02-26T05: 34: 22.294682 + 00: 00 app[web.1]:
2019-02-26T05: 34: 22.680467 + 00: 00 heroku[web.1]: Process left with status 1
2019-02-26T05: 34: 31.636059 + 00: 00 heroku[web.1]: Startup Process with the `npm start` Command
2019-02-26T05: 34: 33.484341 + 00: 00 heroku[web.1]: State changed from start to crash
2019-02-26T05: 34: 33.458183 + 00: 00 heroku[web.1]: Process left with status 1
2019-02-26T05: 34: 33.279088 + 00: 00 app[web.1]:
2019-02-26T05: 34: 33.279111 + 00: 00 app[web.1]:> zenform2@1.0.0 start / app
2019-02-26T05: 34: 33.279113 + 00: 00 app[web.1]:> node ./bin/www
2019-02-26T05: 34: 33.279114 + 00: 00 app[web.1]:
2019-02-26T05: 34: 33.375778 + 00: 00 app[web.1]: internal / modules / cjs / loader.js: 583
2019-02-26T05: 34: 33.375782 + 00: 00 app[web.1]: throw err;
2019-02-26T05: 34: 33.375784 + 00: 00 app[web.1]: ^
2019-02-26T05: 34: 33.375785 + 00: 00 app[web.1]:
2019-02-26T05: 34: 33.375786 + 00: 00 app[web.1]: Error: Can not find module 'express'
2019-02-26T05: 34: 33.375788 + 00: 00 app[web.1]: at Function.Module._resolveFilename (internal / modules / cjs / loader.js: 581: 15)
2019-02-26T05: 34: 33.375794 + 00: 00 app[web.1]: at Function.Module._load (internal / modules / cjs / loader.js: 507: 25)
2019-02-26T05: 34: 33.375796 + 00: 00 app[web.1]: in Module.require (internal / modules / cjs / loader.js: 637: 17)
2019-02-26T05: 34: 33.375797 + 00: 00 app[web.1]: at require (internal / modules / cjs / helpers.js: 22: 18)
2019-02-26T05: 34: 33.375799 + 00: 00 app[web.1]: to the object. (/App/app.js:1:79)
2019-02-26T05: 34: 33.375800 + 00: 00 app[web.1]: in Module._compile (internal / modules / cjs / loader.js: 689: 30)
2019-02-26T05: 34: 33.375802 + 00: 00 app[web.1]: at Object.Module._extensions..js (internal / modules / cjs / loader.js: 700: 10)
2019-02-26T05: 34: 33.375803 + 00: 00 app[web.1]: in Module.load (internal / modules / cjs / loader.js: 599: 32)
2019-02-26T05: 34: 33.375805 + 00: 00 app[web.1]: on tryModuleLoad (internal / modules / cjs / loader.js: 538: 12)
2019-02-26T05: 34: 33.375807 + 00: 00 app[web.1]: at Function.Module._load (internal / modules / cjs / loader.js: 530: 3)
2019-02-26T05: 34: 33.384906 + 00: 00 app[web.1]: npm ERR! ELIFECYCLE code
2019-02-26T05: 34: 33.385464 + 00: 00 app[web.1]: npm ERR! errno 1
2019-02-26T05: 34: 33.387225 + 00: 00 app[web.1]: npm ERR! zenform2@1.0.0 start: `node. / bin / www`
2019-02-26T05: 34: 33.387461 + 00: 00 app[web.1]: npm ERR! Release status 1
2019-02-26T05: 34: 33.387805 + 00: 00 app[web.1]: npm ERR!
2019-02-26T05: 34: 33.388040 + 00: 00 app[web.1]: npm ERR! Failed zenform2@1.0.0 startup script.
2019-02-26T05: 34: 33.388293 + 00: 00 app[web.1]: npm ERR! This is probably not a problem with NPM. There is probably an additional logging output above.
2019-02-26T05: 34: 33.394659 + 00: 00 app[web.1]:
2019-02-26T05: 34: 33.394890 + 00: 00 app[web.1]: npm ERR! A complete diary of this run can be found in:
2019-02-26T05: 34: 33.395027 + 00: 00 app[web.1]: npm ERR! /app/.npm/_logs/2019-02-26T05_34_33_390Z-debug.log
2019-02-26T05: 34: 34.796804 + 00: 00 heroku[router]: at = error code = H10 desc = "application blocked" method = GET path = "/" host = www.zenform.co request_id = e96f9d00-db65-4640-9468-1cf289bf46a2 fwd = "76.102.21.229" dyno = connect = service = status = 503 bytes = protocol = http
2019-02-26T05: 36: 09.766787 + 00: 00 heroku[router]: at = error code = H10 desc = "application blocked" method = GET path = "/" host = www.zenform.co request_id = 7a163af9-f644-4e87-994f-b2b9ac38545c fwd = "76.102.21.229" dyno = connect = service = status = 503 bytes = protocol = http
Stream The log stream has expired. Try Again.

Here is my package.json in the client folder.

{
"customer name",
"version": "0.1.0",
"private": true,
"scripts": {
"start": "react-scripts start",
"build": "react-scripts build",
"test": "reaction-scripts test",
"eject": "react-scripts eject"
}
"proxy": "http: // localhost: 5000",
"eslintConfig": {
"extend": "react-app"
}
"list of browsers":[
    ">0.2% ",
"not dead",
"not ie <= 11",
"not op_mini all"
],
"dependencies": {
"@ material-ui / core": "^ 3.4.0",
"@ material-ui / icons": "^ 3.0.1",
"css-loader": "^ 1.0.1",
"express": "^ 4.16.4",
"jquery": "^ 3.3.1",
"popper.js": "^ 1.14.4",
"prop-types": "^ 15.6.2",
"react": "^ 16.6.3",
"react-dom": "^ 16.6.0",
"react-ga": "^ 2.5.6",
"react-helmet": "^ 5.2.0",
"react-mailchimp-subscribe": "^ 2.0.2",
"react-router": "^ 4.3.1",
"react-router-dom": "^ 4.3.1",
"react-scripts": "2.1.1",
"style-loader": "^ 0.23.1",
"stylized components": "^ 4.1.2"
}
"devDependencies": {
"babel-core": "^ 6.26.3",
"babel-preset-es2015": "^ 6.24.1",
"babel-preset-react": "^ 6.24.1",
"babel-preset-stage-2": "^ 6.24.1",
"nodemon": "^ 1.18.7"
}
}

And then here is the package.json in the main directory of the project.

{
"name": "zenform2",
"version": "1.0.0",
"the description": "",
"main": "index.js",
"scripts": {
"start": "node ./bin/www",
"heroku-postbuild": "cd client && npm install --only = dev && npm install && npm run build"
}
"keywords": [],
"author": "",
"license": "ISC",
"dependencies": {
"body analyzer": "^ 1.18.3",
"dotenv": "^ 6.2.0",
"express": "^ 4.16.4",
"request": "^ 2.88.0"
}
}

Here is a picture of the structure of my file also if it is relevant.

enter the description of the image here

An idea of ​​what I'm doing wrong? If you need more information, I'm happy to answer your questions