We don't yet support invoicing in the app. For now, we recommend you continue using your preferred invoicing tool.
That said, you don't need a fancy tool to send an invoice. All you need is an email containing the following information:
An invoice number
You name and contact information
The name (or company name) and contact information of the customer
A description of the goods or service to be paid for
The date the goods or service were provided
The date of the invoice (this is automatic on an email)
The amount (£) due
Instructions of how the invoice should be paid
When you are paid for an invoice, be sure to classify that transaction in the app so that it's included in your insights and tax return! You can also attach the invoice to the payment for safe keeping.