The code snippets below should be placed in your child theme’s functions.php file. Doing so will allow for you to upgrade Sprout Invoices without losing your customizations. If you’re not sure how WordPress actions and filters work, checkout this wiki, they’re super powerful and help Sprout Invoices fully customizable.
Adding New and Customizing Existing Line Items
Adding a Print page button on estimates and invoices
Redirect to Invoice After Estimate Approval
Convert Percentage Column to Discount (on the front-end)
Set Default Invoice Due Date
Customizing Default Invoice Information – Example: Invoice ID with Custom Date and Number
Customize Invoice ID based on Sequence and Prefix
Creating an Invoice via the API
Creating an Estimate via the API
Create a Project form an Estimate Acceptance
Translating text strings
Getting a user’s estimates and invoices
Creating an invoice programmatically
Redirect if not logged in
Creating a Client (and user)
Creating a payment
Sending an Invoice
Manually Setting Locale
Filter Default Estimation Fields
Customizing Sprout Invoice Templates (via CSS)
Set line items on Estimate Submission
Add CSS to the PDF Generated Invoice
Remove Admin Bar links
Limit Sprout Invoices Post Type Access
Custom CSS for Print Invoices/Estimates
Automatically Send Invoice after it’s Auto Generated
Modifying Icons for PayPal EC purchase option
Adding Additional Columns to the Invoice admin
Adding VAT to Invoices and Estimates
Automatically Approve Submitted Estimate (with Advanced Form Integration Add-on)
Remove Line Item Comments
Change the To: Email for Admin Notifications
Change Post Type Registration – Change “Client” to “Account”