Azure error "Your certificate file was invalid, or the password was incorrect" loading certificate into portal - azure-keyvault

Question

I generated a public_privatekey.pfx via the xero instructions and was able to access a Xero demo file from a Visual Studio solution that used Xerp.Api.Sdk.Core
Now I want to put the certificate in an Azure Key Vault so that I can port my code to an Azure Function App.
However when I try to use the Azure Portal to load the certificate via
Create a secret -> Certificates ->Create a certificate
I get an error
Your certificate file was invalid, or the password was incorrect
I can load the certificate using Powershell.
Connect-AzureRmAccount -tenantid mytenantid
$pfxFilePath = 'C:\OpenSSL-Win64\bin\AzureXeroSync\public_privatekey.pfx'
$pwd = 'mypassword'
$flag = [System.Security.Cryptography.X509Certificates.X509KeyStorageFlags]::Exportable
$collection = New-Object System.Security.Cryptography.X509Certificates.X509Certificate2Collection
$collection.Import($pfxFilePath, $pwd, $flag)
$pkcs12ContentType = [System.Security.Cryptography.X509Certificates.X509ContentType]::Pkcs12
$clearBytes = $collection.Export($pkcs12ContentType)
$fileContentEncoded = [System.Convert]::ToBase64String($clearBytes)
$secret = ConvertTo-SecureString -String $fileContentEncoded -AsPlainText –Force
$secretContentType = 'application/x-pkcs12'
Set-AzureKeyVaultSecret -VaultName 'MyAzureFunctionsVault' -Name 'XeroPfxSecret' -SecretValue $Secret -ContentType $secretContentType
what am I missing using the portal ?

Answer 1

You mentioned this in your question:
Create a secret -> Certificates ->Create a certificate
I think the issue here is that you're starting with "Create a secret". Uploading/Importing a certificate as a secret is a deprecated feature as you can see in screenshot.
Can you try doing the same thing, but starting from "Certificates" and then do an import instead?