Go to Settings > Payment Methods and toggle on Bank transfer.
Enter your account and routing details in the instructions box. This information will be visible to your clients on the invoice when they choose to pay via bank transfer.
Once you've entered your details, click Save to apply the changes.
If you have a payment method enabled (like Cash, Check or Bank Transfer) but haven't added your account details, it will still appear as an option to your clients—but without the necessary information for them to pay you.
To fix this: Visit Settings > Payment Methods, enter your bank account and routing details for each enabled method, and save. If you don't plan to use a payment method, disable it so it doesn't appear on your invoice.