passkit-generator: Getting unsupported file format issue,after pkpass file generate process.

const passCreated = await PassKit.PKPass.from({
    model: `${process.cwd()}/src/BoardingPass.pass`,
    certificates: {
       wwdr,
       signerCert,
       signerKey,
       signerKeyPassphrase,
    },
});

try {
    const buffer = passCreated.getAsBuffer();

    await fs.writeFile('sample.pkpass', buffer);

    this.logger.debug('Pass generated successfully....');
} catch (error) {
    throw Error(error.message);
}

Used this,but getting file format issue on viewing it.