To enable users to add repeating tasks in Salesforce, the administrator needs to do two things: first, enable the creation of recurring tasks in activity settings under setup; second, add the create recurring series of tasks field on the page layouts for tasks. This will allow users to create a series of tasks that repeat based on a specified frequency and end date. References: https://help.salesforce.com/s/articleView?id=sf.tasks_repeating.
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