Saving photos from custom VkLongPoll Python attachments

Hello! I'm trying to make a bot, I need to get an image from the user, and save it in a file. At the moment I can't get a link to the image and this code:

vk_session = vk_api.VkApi(token='токен сообщества')
Lslongpoll = VkLongPoll(vk_session) 
Lsvk = vk_session.get_api()
for event in Lslongpoll.listen():
    if event.type == VkEventType.MESSAGE_NEW and event.to_me and event.text:
        atchs = event.attachments

        if atchs:
            if atchs['attach1_type'] == 'photo':
                photo_id = event.attachments['attach1']
                photo_info = Lsvk.photos.get_by_id(photos=photo_id)
                photo_urls = {size['type']: size['url'] for size in photo_info['sizes']}
                print(photo_urls)

Crashes with an error:

vk_api.exceptions.ApiError: [27] Group authorization failed: method is unavailable with group auth.

Question - how to log in to the bot correctly, and how to write the photo to a file in the future?