To manage recurring invoices, the app would allow users to set up invoice templates that can be automatically generated at specified intervals. When creating a new recurring invoice template, the user would be able to select thebilling frequency such as monthly, quarterly, annually etc. They would also specify the start date for when invoicing should begin, and any specific billing dates (e.g. always on the 15th of the month).

The invoice template would allow the user to include standard items and pricing that should be included on every automatically generated invoice. This could include things like the client name and address, logo, standard services or product line items, terms and conditions etc. Any text, images or formatting could be added to customize the look and content of the template.

For items that may vary between invoices like quantities, unique product or service codes, project names, users can set up “template fields” that will be populated dynamically when invoices are created. For example, a field could be added for total hours worked on a project that month that would pull data from a projects module to populate the right value.

Users would be able to add as many customizable fields to the templates as needed to cover all variables that may change. Default values could also be set for fields that often stay the same to reduce data entry on recurring invoices.

Once the recurring invoice template is set up, the app would automatically generate new invoices based on that template according to the specified billing frequency. It would pull any dynamic fields from the relevant source data like projects, timesheets or products tables. Invoices could be generated either on the stated billing date, or a certain number of days before to allow for reviewing and sending in advance.

As invoices are created, they would be recorded in an invoices module where users can view, print, email or export any past or current invoices as needed. Invoices would also link back to the clients or jobs they were created for so payment history and balances could be tracked per client/project.

Users would have the ability to edit invoice templates over time as needed. Any changes made would apply dynamically to future invoices created from that template, but not retroactively change past invoices already issued. Templates could also be inactivated so they stop generating new invoices without deleting the template entirely.

For invoices that don’t need to be recurring, the app would allow users to manually generate one-off invoices based on customizable invoice templates. This could cover non-recurring work as well as providing a backup solution if there was ever an issue with automatically generated recurring invoices.

The invoice templates themselves could be fully customizable in terms of colors, logos, fonts, section layouts and more. Users could access a drag-and-drop interface to design and format their templates as needed without any technical constraints. Multiple templates could be saved to offer clients/departments variety or to match various brand styles.

Some key considerations for the invoicing templates module would include:

Role-based access permissions to manage templates and invoices

Version control for templates with audit trails of any changes

Integration with other systems for pull billing variables like project details, time entries etc

Conditional logic and calculation fields for auto-populating totals

Cron job/scheduled tasks to generate recurring invoices on time

Email notification/reminders of upcoming or overdue invoices

Comprehensive search, filters and reporting on past invoices

PDF export and storage of issued invoices for recordkeeping

Payment records and balance due tracking per client/job

Invoice approval workflows for multi-user sign-offs

Template library/gallery for easy access and organization

Guidance and help documentation for common user tasks

With these types of features, the app could provide a robust yet flexible solution for businesses, consultants, freelancers and others to create and track both recurring and one-off invoices professionally and efficiently through customizable invoicing templates. The ability to automate reoccurring work would save time while still ensuring invoices are customized to clients through adjustable fields and formatting options.