[SOLVED] Error adding payment method: "Failed to create setup intent! Error: Unexpected error."

[SOLVED: Muse Hub support goes here: https://support.musehub.com/hc/en-gb]

I cannot add payment methods to my Muse Hub account.

The on-screen error message shows "Failed to create setup intent! Error: Unexpected error."

The fetch returns this:

{
    "errors": [
        {
            "message": "Unexpected error.",
            "locations": [
                {
                    "line": 3,
                    "column": 3
                }
            ],
            "path": [
                "customer_createSetupIntent"
            ]
        }
    ],
    "data": null
}

I have tried this on both my existing Google login as well as a newly-created direct email account.