Include QuoteID/InvoiceID in either Invoices or Quotes endpoint to allow analysing
Our customers need to be analyse Quotes and Invoices and link both with each other. Unfortunately, while you can create a sales invoice from a quote, there is no linking identifier between the two.
It would be good to include the InvoiceID in the Quotes to know which invoice was create from the quote. If a quote can be invoiced multiple times, it would be good for this to be an Invoices collection.
It would also be good to include the QuoteID in the Invoices endpoint to know this invoice originated from a quote and which.

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Data Inseyets commented
This is a great idea. its very important for us to see the burn down of quoted values for our clients. If we quote for 3 months of work and we issue 1 invoice per month then particularly with the last one we need to make sure we don't invoice over what the quoted amount was.