Public facing IP addresses - different results from different places (browser vs cmdline)

Question

So visiting https://www.whatismyip.com/ in the web browser (Google Chrome) shows your IPV4 address

But I get a completely different IP address If I inspect and get the code for the same POST request

I am connected to a [workplace] VPN, and the request via browser correctly recognizes the VPN provider and shows their IP address (which is what I want).

But if I make the same request from my cmdline (powershell for example), I get the IP address of the modem in my home.

$session = New-Object Microsoft.PowerShell.Commands.WebRequestSession
$session.UserAgent = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/122.0.6261.112 Safari/537.36"
Invoke-WebRequest -UseBasicParsing -Uri "https://api.whatismyip.com/wimi.php" `
    -Method "POST" `
    -WebSession $session `
    -Headers @{
    "Accept"             = "*/*"
    "Accept-Encoding"    = "gzip, deflate, br, zstd"
    "Accept-Language"    = "en-US,en;q=0.9,te;q=0.8"
    "DNT"                = "1"
    "Origin"             = "https://www.whatismyip.com"
    "Referer"            = "https://www.whatismyip.com/"
    "Sec-Fetch-Dest"     = "empty"
    "Sec-Fetch-Mode"     = "cors"
    "Sec-Fetch-Site"     = "same-site"
    "sec-ch-ua"          = "`"Chromium`";v=`"122`", `"Not(A:Brand`";v=`"24`", `"Google Chrome`";v=`"122`""
    "sec-ch-ua-mobile"   = "?0"
    "sec-ch-ua-platform" = "`"Windows`""
}

Anyone know what kind of magic this is? I am looking to find the IP address of the VPN provider. TIA