In my last software job, you’d get fired for going public-facing live with a site that hadn’t gone through sufficient offline testing and the released version had errors like this.
Ohh, no no this is just the HTTPS request that keeps failing with 503 Service Unavailable. I am using the same link (SketchUp Extension Warehouse) to access the signing service.
It is quite unfortunate that it has been a couple of days but the signing service is still broken for me, reached out to developer-support@sketchup.com, hopefully they will also help to resolve this issue!