S3 Object user defined metadata not getting updated using PUT request on API

I am following this documentation (https://aws.amazon.com/premiumsupport/knowledge-center/api-gateway-upload-image-s3/) to upload S3 object using API gateway, with no Lambda in between. This works using Postman. The object gets uploaded, but the user-defined metadata is not been reflected on the object when I check on the console.

I am trying to add user-defined metadata to headers, but that seems to be not working. I also tried to add "x-amz-meta-{key}": "{value}" in the form-data field of the body, and that did not work as well. Any recommended solution? I am trying to avoid using Lambda in between API G/W and S3. Thanks in advance!