You can customize the Xero Invoice in various ways. This also depends on which edition of Breadwinner you are on, Basic, Professional, Business, or Enterprise.
Please note that because the Invoice record is replicated from Xero, rather than created in Salesforce first, it isn't possible to use Workflow, Process Builder, or Apex Triggers to accomplish pre-populating the fields. Instead, you can use the methods below.
Additional information is below, but this video provides an overview.
Basic Edition of Breadwinner
With the Basic Edition of Breadwinner you can pre-populate two fields on the Invoice, Invoice Date and Due Date. The Invoice Date is today's date, and the Due Date is set based on the Invoice Date. You can set the Due Date in the Invoice Configuration section of the Breadwinner tab.
Additionally, you can set the default Account Revenue Code for all invoices.
Professional Edition of Breadwinner
With the Professional Edition of Breadwinner, you can populate all of the Invoice level fields from custom fields. So, the Invoice Date, Due Date, Invoice Reference, and Branding Theme can be set from standard and custom fields on the Opportunity. Please note that for Branding Theme, a perfect match text is required.
Business Edition of Breadwinner
With the Business Edition of Breadwinner, you can populate the Invoice Line Items from custom fields on the Opportunity Product. These can be formula, lookup, or text fields. With formula fields, you can reference the Opportunity, or the Product, or the Salesforce Account. This gives you a tremendous amount of power to write complex business rules and have them populate your Invoice line items.
This also populates Tracking Categories, but those must be first created and set in Xero.
A perfect text match is required for all matching. This includes Tax Codes, should you wish to populate them, which are not just "2%" but instead are "Sales Tax ( 2.00% )" or similar.
With the Enterprise Edition of Breadwinner, you can populate anything on our Invoice page with virtually any object, object field, or child object / child object field.
So, you can us an entirely custom object and custom child object, or a standard object and a custom child object, or a standard object and custom fields on that object. You can even have fields on the single record populate multiple line items on the Invoice.
Enterprise Edition features can be enabled as part of your free trial, but you'll need to contact us to enable them.