Prepare signing/verifying module from node js crypto

I'm working on a node crypt module that will signing/verifying. I have managed the verifying module:

'use strict';

const crypto = require('crypto');
const fs = require('fs');
const path = require('path');

const publicKey = fs.readFileSync(path.join(__dirname, 'key.pub'));
const encryptDataPath = path.join(__dirname, 'encryptData.txt');
let encryptData = fs.readFileSync(encryptDataPath).toString();

//console.log(encryptData);


// start decoding
const plainEncryptData = Buffer.from(encryptData, 'base64').toString();


const [signatureb64, contentb64] = plainEncryptData.split('\n');


const signature = Buffer.from(signatureb64, 'base64');
const content = Buffer.from(contentb64, 'base64').toString();

const verifier = crypto.createVerify('RSA-SHA256');
verifier.update(content);
verifier.end();

const isValid = verifier.verify(publicKey, signature);

if (!isValid) {
    console.log('not valid');
} else {    
    console.log(content);
}

Here is the public key (pub.key):

-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEApuI1XlPkYos3WsSeVPtS
l1Q2k8GnLEO5vFZ4EuSghMbqI+yE0tWVEaiptdV3KgERaALRXmH+IFrHqvSRjKQC
1ORUarBU5ntWbNEr713R3K0BPOzz9OOoWHdk+Wmr4ViOTk0iD1u4bw/97RpyMoBm
+pXeBLHbEESK2kelk+LEmKUoY5nXp6KzZV5wxgD5QweZheU7mjXL5WMpIBJva8kp
RZMYXEF+uSZIep0q5FHEo2AazGUMAU3GjY/dpXisLmtleOa1xlKZmkvaXl/D2Mhb
BBqPbDMa72ToZg2J8K5UP9zXUP41FHr7o9rwSJ2uOkuZPg5nhDXeoVbrJwxP/U1M
nQIDAQAB
-----END PUBLIC KEY-----

Here is encryptData.txt (encrypt data)

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

Now, I am trying to create its signing module which will create encrypt data as same as encryptData.txt:

'use strict';

const crypto = require('crypto');
const fs = require('fs');
const path = require('path');

const publicKey = fs.readFileSync(path.join(__dirname, 'key.pub'));

let content = {}
content.type = "bronze";
content.customerId = "16COVRSc9x21fCHnE";
content.expireAt = 1626576362000;
content.isTrial = true;
content.licenseKey = "c9295b69-bee6-431a-8d7d-0b740f01ca2d";
content.createdAt = 1625366769531;


const encryptDataPath = path.join(__dirname, 'encryptData.txt');
let a = fs.readFileSync(encryptDataPath).toString();

// signing
const signer = crypto.createSign('RSA-SHA256');
signer.update(content);
signer.end();

const signature = signer.sign(publicKey, 'base64');

console.log('sign: ', signature);
 

But when I run this encrypt module, it is throwing this error:

internal/crypto/util.js:97
    throw new ERR_INVALID_ARG_TYPE(
    ^

TypeError [ERR_INVALID_ARG_TYPE]: The "data" argument must be one of type string, Buffer, TypedArray, or DataView. Received type object
    at Sign.update (internal/crypto/sig.js:49:10)
    at Object.<anonymous> (/home/ubuntu/www/node-encrpt/encode.js:23:8)
    at Module._compile (internal/modules/cjs/loader.js:959:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:995:10)
    at Module.load (internal/modules/cjs/loader.js:815:32)
    at Function.Module._load (internal/modules/cjs/loader.js:727:14)
    at Function.Module.runMain (internal/modules/cjs/loader.js:1047:10)
    at internal/main/run_main_module.js:17:11 {
  code: 'ERR_INVALID_ARG_TYPE'
}

I can not figure out why this occurs.

How can I complete the encrypt module?