discord.js v13 bot uptime

Question

I made some bot uptime code but got an error showing 52 years ago The code is below.

const style = 'R'
const starttime = `<t:${Math.floor(client.readyAt / 1000)}` + (style ? `:${style}` : '') + '>'

client.on('messageCreate' , message=>{
    if(message.content == "!uptime"){
        message.reply(`uptime!\n uptime : ${starttime}`)
    }
})