The hyperlink contained in the body of the email alert for a Purchase Request is configured separately according to the Purchase Request Approval Stages.
It could be that the URL is a malformed link or contains an invalid redirect to another page.
You should be able to find the Purchase Request for approval within Financial Operations, as the Purchase Request Approver by following the steps below:
From Workspace click the nine dot menu and select the Financials Operations app and database
On the Purchasing tab, in the Authorisation section, select the appropriate approval ThumbsUp icon with the required Purchase Request Type name. The correct webpage should open
Locate the Purchase Request ID and approve or reject accordingly.