Sometimes when you try to install Clockwork Pro (or any other paid app in the Atlassian Marketplace), the installation process takes a long time, and soon after it finishes, the app is uninstalled. The timeframe of this cycle is usually around 4 minutes.
This is because Atlassian Marketplace deems your instance unfit for paid apps, most likely because the billing details are missing or incorrect.
First, confirm that this is the case by checking the App manager logs.
Go to Manage your apps in the top menu bar:
Click on Audit logs:
Look for a cycle of installations followed by uninstallations after roughly 4 minutes. If this pattern is present, the uninstallation is caused by the Atlassian Marketplace.
The most common cause is an issue with payment method details in the billing settings. If updating those does not solve the issue for you, please reach out to the Atlassian Support Team for further guidance.