Fromni. Notifications & Pipedrive.
You can set up an automation which will send messages before or after certain time of the activity.
For example, you added in Pipedrive “Meeting with the customer” and exactly one day before the customer will receive the text: “Hello from Fromni. This is a reminder that we have a meeting tomorrow at 1pm.”
You can find detailed instruction here: https://fromni.com/help/integrations/pipedrive-instruction