from requests import PreparedRequest

# ...

@client.event
async def on_member_join(member):
    if config['join_leave_message'] is True:
        channel = client.get_channel(config['join_leave_channel'])
        embed = discord.Embed(colour=discord.Colour.green())
        req = PreparedRequest()
        req.prepare_url(
            url='https://api.xzusfin.repl.co/card?',
            params={
                'avatar': str(member.avatar_url_as(format='png')),
                'middle': 'welcome',
                'name': str(member.name),
                'bottom': str('on ' + member.guild.name),
                'text': '#CCCCCC',
                'avatarborder': '#CCCCCC',
                'avatarbackground': '#CCCCCC',
                'background': '#000000' #or image url
            }
        )
        embed.set_image(url=req.url)
        await channel.send(embed=embed)