Error: Route.post() requires a callback function but got a [object Undefined]

[nodemon] starting `webpack --mode=development --config webpack.config.server.js && node ./dist/server.generated.js`
Hash: e82da5c29b9639def338
Version: webpack 4.42.1
Time: 1456ms
Built at: 20/12/2021 12:06:26
                               Asset     Size  Chunks             Chunk Names
08179a3b58e30f3c8c4fed34a9a3e2f8.jpg  790 KiB          [emitted]
                 server.generated.js  183 KiB    main  [emitted]  main
Entrypoint main = server.generated.js
[0] multi ./server/server.js 28 bytes {main} [built]
[./client/MainRouter.js] 2.02 KiB {main} [built]
[./client/theme.js] 1.39 KiB {main} [built]
[./config/config.js] 1.21 KiB {main} [built]
[./node_modules/webpack/buildin/harmony-module.js] (webpack)/buildin/harmony-module.js 573 bytes {main} [built]
[./server/devBundle.js] 1.43 KiB {main} [built]
[./server/express.js] 3.26 KiB {main} [built]
[./server/routes/auth.routes.js] 1.13 KiB {main} [built]
[./server/routes/course.routes.js] 1.65 KiB {main} [built]
[./server/routes/user.routes.js] 1.41 KiB {main} [built]
[./server/server.js] 662 bytes {main} [built]
[./template.js] 1.66 KiB {main} [built]
[@material-ui/styles] external "@material-ui/styles" 42 bytes {main} [built]
[body-parser] external "body-parser" 42 bytes {main} [built]
[mongoose] external "mongoose" 42 bytes {main} [built]
    + 74 hidden modules
C:\Coding\master-baguette\node_modules\express\lib\router\route.js:202
        throw new Error(msg);
        ^

Error: Route.post() requires a callback function but got a [object Undefined]
    at Route.<computed> [as post] (C:\Coding\master-baguette\node_modules\express\lib\router\route.js:202:15)
    at Module.eval (webpack:///./server/routes/course.routes.js?:21:41)
    at eval (webpack:///./server/routes/course.routes.js?:46:30)
    at Module../server/routes/course.routes.js (C:\Coding\master-baguette\dist\server.generated.js:420:1)
    at __webpack_require__ (C:\Coding\master-baguette\dist\server.generated.js:21:30)
    at Module.eval (webpack:///./server/express.js?:19:80)
    at eval (webpack:///./server/express.js?:136:30)
    at Module../server/express.js (C:\Coding\master-baguette\dist\server.generated.js:360:1)
    at __webpack_require__ (C:\Coding\master-baguette\dist\server.generated.js:21:30)
    at eval (webpack:///./server/server.js?:3:66)
    at Module../server/server.js (C:\Coding\master-baguette\dist\server.generated.js:444:1)
    at __webpack_require__ (C:\Coding\master-baguette\dist\server.generated.js:21:30)
    at eval (webpack:///multi_./server/server.js?:1:18)
    at Object.0 (C:\Coding\master-baguette\dist\server.generated.js:478:1)
    at __webpack_require__ (C:\Coding\master-baguette\dist\server.generated.js:21:30)
    at C:\Coding\master-baguette\dist\server.generated.js:85:18
[nodemon] app crashed - waiting for file changes before starting...