PATCHing secrets with PowerShell

When using PowerShell to patch my secrets

I include this payload:

Payload: {
    "path":  "EncId",
    "op":  "replace",
    "value":  "MB34Changed"

for this URI: ourvaulturi/v1/enginename/data/secretname

This is my PS command:
$response = Invoke-RestMethod -Headers $header -ContentType 'application/json' -Method PATCH -Uri $uri -Body $payload

$header includes my Token and Namespace
I get a (415) Unsupported Media Type error

Any ideas or help here?
I don’t want to use PUT because it overwrites ALL values in my secret and I only want to update a single value.

Seems that, yes, v1 and data are required in the URI: https://ourvaulturi/v1/enginename/data/secretname

The Content-Type needs to be set in the header:

$header = @{

And the payload needs to be formatted as:

$payload = 
        } | ConvertTo-Json

Then, the Invoke-RestMethod need to look like this:

Invoke-RestMethod -Headers $header -Method PATCH -Uri $uri -Body $payload