Problem
The Recurring Service Complete button is missing because the job's invoice has been exported. Once an invoice is exported, ServiceTitan limits changes to the job.
Solution
Check to see if the job's invoice has been exported.
Go to the job page.
Click the invoice to see if it has been exported.
When an invoice is exported, ServiceTitan restricts further edits to the job. This includes marking the job as complete for recurring services. If you need to make changes to a job after the invoice has been exported, consider creating a new job entry for the recurring service. This allows you to bypass the restrictions.
Note: It's important to manage invoices carefully to avoid restrictions on job modifications.