The client is still deciding
Use a quote when the client still needs to approve the work, the scope, the price, or the timing. The document is there to support the decision.
Most billing confusion here is not about file format. It is about timing. If the client is still deciding, you usually need a quote. If the work or sale is ready to be charged, you need an invoice. If the approval is done but a structured prepayment request still has to happen first, that is where proforma usually enters the workflow.
Use a quote when the client still needs to approve the work, the scope, the price, or the timing. The document is there to support the decision.
Use proforma when the client has effectively said yes, but you still need a structured document for deposit collection, approval-stage billing, or pre-shipment payment handling.
Use the invoice when the document has to request real payment for work or goods that are already ready to be billed.
Send a quote when the client still needs to decide whether to approve the work, the price, or the scope.
Send an invoice when the billing step is real and the document needs to request actual payment.
That is usually where a proforma invoice belongs. It sits between quote and final invoice when prepayment or approval-stage billing still matters.
Most users should move either to the quotation template, the quote-vs-invoice help page, or the proforma invoice page depending on the stage they are in.
Start with quotation if approval is still open, use proforma if payment needs a middle step, and use the final invoice only when the billing event is ready.