You may get a reintegration failure if you have previously connected your Google Workspace to Push. To fix this, follow the steps below (these steps should be followed by the user who did the previous integration, or a Workspace admin):
Go to the Security section of My Account.
Find the tile called "Third-party apps with account access". Click "Manage third-party access":
Under "Third-party apps with account access", find the Push Security app:
With the Push Security app expanded, select "Remove access":
You should now be able to successfully re-add the Google Workspace Push Security integration.