Push fails on Oracle Cloud registry

[alessiofiore]

I'm trying to build and push an image on Oracle Cloud registry, but it fails with the following error:

failed to solve: rpc error: code = Unknown desc = fra.ocir.io/***: failed to authorize: failed to fetch oauth token: unexpected status from GET request to https://fra.ocir.io/*** 400 Bad Request

This is the buildx command:

docker buildx build --platform linux/amd64,linux/arm64,linux/arm/v7 -t fra.ocir.io/*** --push .

This is my config.json that works for any other simple push without using buildx:

{
    "auths": {
            "fra.ocir.io": {
                    "auth": "***"
            }
    }
}

It fails even if before I do docker login on Oracle cloud.
It works fine if I run the command above pushing on docker hub.

Here some details about the version:

Client: Docker Engine - Community
Version: 19.03.5
API version: 1.40
Go version: go1.12.12
Git commit: 633a0ea
Built: Wed Nov 13 07:25:41 2019
OS/Arch: linux/amd64
Experimental: true

Server: Docker Engine - Community
Engine:
Version: 20.10.6
API version: 1.41 (minimum version 1.12)
Go version: go1.13.15
Git commit: 8728dd2
Built: Fri Apr 9 22:43:57 2021
OS/Arch: linux/amd64
Experimental: true
containerd:
Version: 1.4.4
GitCommit: 05f951a3781f4f2c1911b05e61c160e9c30eaa8e
runc:
Version: 1.0.0-rc93
GitCommit: 12644e614e25b05da6fd08a38ffa0cfe1903fdec
docker-init:
Version: 0.19.0
GitCommit: de40ad0