You may get an AWS reintegration error if you already have a stack in your account called PushSecurityStack. This could happen if you removed an AWS integration in the Push Security web application, but not within your AWS account.
In this scenario, you can safely delete the stack in your account by following the steps below:
Go to CloudFormation service page for the region containing the stack.
Select PushSecurityStack in the list on the left and press the delete button:
Once the delete is complete, you should be able to successfully re-add the Push Security AWS integration.