If you received a notification advising you have an invoice to review for approval and when you log into BeanworksAP you can't find/see it, likely this is because the invoice has already been approved by another approver.
For example the below approval channel states the Invoice can be approved by either one of the two approvers. If Neha approves/rejects the invoice first then Brittney will not have to review the invoice and the invoice will not show in her approvals tab as the approval has already been completed by Neha.
The other possibility is that you have a filter turned on, or have unselected some OUs which is why you cannot see the invoices. Ensure you have all custom filters turned OFF and all OUs Selected on your Approval Tab.
Finally, another possibility is that someone has reset the invoice that was for your approval since the email was sent to you.