Approval request on slack

Hi there,
I’m trying to set up an approval process and having trouble with that.
The trigger is to watch Xero invoices, then filter them out, for relevant one download attachment (done up to this point).
I’d like to send a message to Slack consisting of the attachment from Xero, Text fields from the invoice and an ‘Approve’ and ‘Reject’ button. Clicking on one of those would be a webhook trigger for the next process.
What’s the best way to send this kind of message?

Any help would be very much appreciated.