Can't customize Access login page

I’m trying to customize the login for Cloudflare Access to add my business brand.

But when I log into the customization editor this is what appears:

I only signed up for one user. Although I provided credit card details, it seems to me as if anything less than five seats does not incur charges. I mention this in case it is a premium-only feature.

The error reads:

API Request Failed: GET /api/v4/zones/42d97996772e090d20cbdd85ff0294dc/edgeauth/preview?backgroundColor=%23eee&logoURL=& (undefined)

Is there a possible explanation for this behavior? I can’t seem to access the editor itself with the error messages superimposing themselves.

Happening for me to, likely an intermittent issue. I’ve made a support ticket [1827023] for this.