FINSYNC's projects module allows you to create invoices directly from the project. Those invoices are already for the customer of the project and allow you to pull phases that you are ready to bill and/or expenses that you are ready to bill into the retainer.
If FINSYNC is forcing you to create a retainer, it means you have not yet set up any billable items. You need to either add a billable phase (hourly by phase, hourly by task, or fixed rate by phase) or add some expenses.
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