...
Activate “Enable uploading invoices” from: Administrator > Web administrator > Configuration > Settings
(Optional) “Invoice upload mandatory for approval/submit” will force resources to upload an invoice before they can submit or approve their reports.
...
(Optional) “Approval submit is mandatory for Invoice upload” will force resources to submit or approval their report before they can upload an invoice.
...
Uploading and managing invoices
...
A reminder to upload an invoice can be sent to a resource using the “Send invoice reminder email” column (1), or sent to all resources in the current page using the “Send invoice reminders” icon (2) on the bottom of the page.
...
This can be done from both Finance > Monthly resource report approval status and Finance > Resource report (Finance).
...