Google cloud storage client api not working for patch

Google cloud storage client api not working for patch

I tried updating header of an object by using API explorer (as well as
client library) by giving metadata object as header keys and values.
I only received error respond
{
error": {
"errors": [
{
"domain": "global",
"reason": "invalid",
"message": "Invalid argument."
}
],
"code": 400,
"message": "Invalid argument."
}
}
The request is:
PATCH
https://www.googleapis.com/storage/v1beta2/b/mbi-figure/o/infovilla_paypal.png?key={YOUR_API_KEY}
Content-Type: application/json
Authorization: Bearer ya29
X-JavaScript-User-Agent: Google APIs Explorer
{
"metadata": {
"title": "Kyaw"
}
}