secure the 2-stage approval application using SharePoint & Power Apps & Power Automate

[john john]

We have a travel request application. where a user submit a request which should go into 2 stages of approval process before it gets Final Approval.

Now we did the following:-

1. Create a SharePoint list which contain those fields; Title, Description, StareDate, EndDate, FirstApproval (the requestor direct manager), SecondApproval (the requester regional approval), Statues (system-generated with those options; open, first-approved, second-approved, Final-Approved).

2. Power Apps, which send emails to the first-approval and the second-approval users , and show-hide the Approved & Reject buttons based on the item status.

3. Power Automate,to set item-level permissions, so for example when the item needs first-approval only the approval's direct manager can edit the item, while all stakeholders can read-only.

now the process is not 100% secure, as a requestor using API call or using SharePoint built-in forms, can easily create a new request and define its status as Final-Approved. so in other words the requestor can bypass the Power Apps business logic. so how we can secure our process? so if an item has a status = "Final-Approved", then we can 100% sure that it actually went through the 2 approvals users? Thanks