I'm looking to attach a procurement order to a task. It is good for people in development, production, and FA to stay on the same page on an acquisition. Off the top of my head, I was thinking of Quickbooks, an attached PDF/Word file, or a hyperlinked image of the document. The only other thing I could think of was PayPal receipts, but it doesn't work in all situations. I saw a few apps in Jira, Clerks Invoices, Worklog360, BillWize, but it looked like it would require a migration of financial information. After a quick look through, BillWize offered invoice integrations through QuickBooks and it is free up to 10 users then $1.50 per user. Just remember to segment out the access so it doesn't skyrocket pricing.
If you know a standard or best practice better than this, drop a comment please.