I can observe there is a mix-up between global headers and path based headers. You seem to be missing extra information when specifying a path based header. You omitted the Path and Method for the header the and have only added the Key and Value for the header.
"transform_headers": [
{
"add_headers": {"x-tyk-authorization": "foo"},
"path": "API PATH/SUB PATH",
"method": "YOUR HTTP METHOD GOES HERE"
}
]
You can also use the global_headers, but this means that all API calls regardless of the sub path get injected with the header. This may not be ideal.
"global_headers": {
"x-tyk-authorization": "foo",
}