How can I create receipts for payments received through PayPal without using third party software like Invoice Ninja?

There is no native support for custom field validation for duplicates in InvoiceNinja. However, this type of validation for product entries can be added using scripts or the API.

To customize your invoice or quote design in InvoiceNinja, follow the steps given below:

• Open your InvoiceNinja account
• Navigate to 'Settings'
• Press on the 'Invoice Design' option
• Now you can fully modify the layout, colors, and fields of your invoices and quotes.

To change which columns show in the different modules in InvoiceNinja, follow the steps given below:

• Open your InvoiceNinja account
• Navigate to 'Settings'
• Modify the display options under the modules and choose which columns to display or hide.

To make the invoice always included as a PDF attachment in the email in InvoiceNinja, follow the steps given below:

• Open your InvoiceNinja account
• Navigate to 'Email Settings'
• Enable the option to always attach invoices as PDFs to outgoing emails

To charge late fees or percentages for overdue invoices in InvoiceNinja, follow the steps given below:

• Open your InvoiceNinja account
• Navigate to 'Settings'
• Click on 'Invoice Settings'
• Enable the option to add ‘late fees’ or a ‘percentage charge’ for overdue invoices, which will be automatically applied.