I'd like to share some insights about the message prompt ""This will remove any linked transactions."
The steps provided by my colleague will only apply on a regular invoice. If you're converting from a quote, you'll get this prompt.
In this case, you can go back to your quote and change the status to pending. Then change your customer to project. Let me guide you how.
Once done, create an invoice out of your project. This way, your product/service items won't get deleted.
On that same page, you can edit or customize your invoice. Feel free to read this article before emailing your invoice to your customer.
Please don't hesitate to reach out anytime if you have other questions in mind.