This issue happens in two cases:
1- request body is too large and server cannot process this large data. this will serve it
app.use(express.json({limit: '50mb'}));2- req.cookies is too large. When testing different next.js applications on the same browser, each time each app was starting on a different port if there were running some apps. Same app might end up starting at port 3000-3005 range. That means if your app saves cookie, that cookie will be saved for each port. Let's say you started 5 different apps at localhost:3000, and each one saved a cookie. If you make a request, all the cookies will be attached to the request object, in this case you will not able to process even small size of post.body. Solution is you have to delete all the cookies
