Adding my two cents for any who come here late to the game like me. Hopefully this will help.
Our workaround: rather than deleting and then recreating the invoice to get it into the project, we tried copying the invoice and changing customer to the project. That worked, the line items and numbers did not wipe out to zero. Save new invoice. Insert happy dance. We then went to the payment, deselected applying it to the original invoice and selected applying it to the newly created copy invoice (that is in the project). Another happy dance. Then simply went and voided the original invoice. Happy dances all around.
This way, we didn't have to retype or redo anything else, and it left the old intact until we were satisfied with our changes (never delete first! lol). More->Copy->Change customer to project->Save. Done.
Another two cents, if it helps: Someone above mentioned not wanting to create a project first before knowing whether they were going to actually get a project out of it: we get this too, we're a family owned flooring business and we have some that decide to go elsewhere or just don't want to move forward for whatever reason--it's the nature of bidding. We had this same discussion, but ultimately decided it was far more beneficial to create everything, going forward, as a project, whether it's a sure thing or not. Otherwise, your books are a mess of sub-customers and projects and trying to retroactively move everything over, it's just a cleaner way to go about it and drastically reduces administrative time/labor. When we get a new RFP, whether residential or commercial, we simply go create a project (done in seconds). If they're a customer we've never worked with before, we can add them in right there from the project creation screen, and their status is simply "not started". Then if they say yes, the project moves to "in progress". If they say no, the project moves to "canceled". If they want something different, they just get a new estimate in the project with a note in the memo field that it's, for example, "Tile" where the other is marked "Carpet", etc.
We chose *not* to convert completed jobs into projects because that would be an administrative nightmare (subcustomer hayday from desktop). But for all current and future, projects it is.
Ultimately, starting every new thing from the projects module is quicker and cleaner both in the starting of it (adding customer, creating estimate, etc) *and* when the customer makes a decision (everything is already there, nothing to be moved or changed except status).
If you're worried about having too many projects to sort through, the search bar inside your projects module makes that concern moot. Simply start typing and it narrows down with every letter typed. We have only just switched to quickbooks online from desktop and we have roughly a hundred projects. I don't have to scroll to find anything, i just start typing what i'm looking for. The star feature is also handy, we use it for any projects that crews are actively working on (even though we don't need to because of the search function). Makes those quick access and they appear at the top, so the first dozen in the list are our "being installed right now" projects.
