You can use Replicon to track billable amounts and to invoice clients. Refer to How billing works for information on how to set up Replicon for billing.
Create Fixed Bid or rate-based Time & Materials projects that employees enter billable hours and expenses against
Define user, department, project, and role-based rates at the system-level, then customize how they’re applied to each project
Track billable amounts over time in the interface and in reports
Assign project managers and client reps as approvers so you’re confident that items have been billed appropriately
Invoice clients, and track the status of invoices from Draft to Paid
Track productivity & profitability in reports
Transfer billing data to third party applications