You want the PubSub commerce topic outlined here: https://dev.twitch.tv/docs/v5/guides/PubSub/
But yes, seems that there is a UserNotice attached to it (still) as well
Collected and JSON formated (sorry I don’t have the RAW IRC line)
{ badges: [ [ 'subscriber', '0' ], [ 'premium', '1' ] ],
color: '#A60808',
display_name: '<removed>',
emotes: true,
id: '<removed>',
login: '<removed>',
mod: '0',
msg_id: 'purchase',
msg_param_asin: 'B06XP9TRLC',
msg_param_bits: '10',
msg_param_channelID: '<removed>',
msg_param_crateCount: '1',
msg_param_emoticons: '158655',
msg_param_imageURL: 'https://images-na.ssl-images-amazon.com/images/I/819PHGQ9LBL.jpg',
msg_param_title: 'Darkest\\sDungeon',
msg_param_userID: '<removed>',
room_id: '<removed>',
subscriber: '1',
system_msg: 'Purchased\\sDarkest\\sDungeon\\sin\\schannel.',
tmi_sent_ts: '1498394697011',
turbo: '0',
user_id: '<removed>',
user_type: true }
It would seem that the UserNotice provides some additional information over the pubsub topic, such as the Crate contents if a crate is opened, assuming the crate(s) was opened before the user runs the share dialog, so you also gotcha watch for a message here.