Base64 string bigger than ca 76456 bytes is not send via axios post request

I try to send base64 string via axios post request

  const sendData = async () => {
    if (newImg) {
      console.log(fileSizeInBytes(newImg));

      const result = await axios.post(
        `${process.env.REACT_APP_API}/uploadData`,
        {
          type: "image",
          data: newImg,
          userId: user._id,
        },
        {
          headers: {
            authtoken,
          },
        }
      );
      try {
        console.log("data", result.data);
        setImageUrl(result.data.url);
      } catch (error) {
        console.log("error", error);
      }
    }
}

Here I have a function which calculates base64 string size:

function fileSizeInBytes(base64) {
    const base64String = base64.replaceAll("=", "");
    const bytes = base64String.length * (3 / 4);

    return bytes;
  }

But the base64 string is sent only if it’s size is not bigger than ca 76456 bytes. The problem is clearly with the size of the string-if it’s smaller then it gets through.
Here is also my serverside setup

const express = require("express");
const app = express();
const dotenv = require("dotenv");
const mongoose = require("mongoose");
dotenv.config();
const bodyParser = require("body-parser");
const cors = require("cors");

const authRoutes = require("./routes/auth");
const userRoutes = require("./routes/user");
const cloudinaryRoutes = require("./routes/cloudinary");
const chatRoutes = require("./routes/chat");
const messageRoutes = require("./routes/message");

mongoose
  .connect(process.env.MONGO_URI)
  .then(() => console.log("DB connected!!"));

mongoose.connection.on("error", (err) => {
  console.log(`DB connection error: ${err.message}`);
});

app.use(bodyParser.json());
app.use(cors());

app.use("/api", authRoutes);
app.use("/api", userRoutes);
app.use("/api", cloudinaryRoutes);
app.use("/api", chatRoutes);
app.use("/api", messageRoutes);

app.use(function (err, req, res, next) {
  if (err.name === "UnauthorizedError") {
    res.status(401).json({
      error: "Unauthorized",
    });
  }
});

const port = process.env.PORT || 5000;

app.listen(port, () => {
  "Server is up and running on port " + port;
});

Is it an axios problem? What am I doing wrong here?