Edge Extension Publish/Upload API returns 500

I've just migrated from v1 to v1.1 of the https://learn.microsoft.com/en-us/microsoft-edge/extensions-chromium/publish/api/using-addons-api?tabs=v1-1#uploading-a-package-to-update-an-existing-submission.

Since then I'm only receiving HTTP 500 responses from the API. All credentials are correct since I've also received some 4xx before that.

The following is a curl req & res. All sensitive params are redacted. The exact same extension package gets distributed to the Chrome store. Nothing really changed in the extension package from v1 to v1.1.

> POST /v1/products/.../submissions/draft/package HTTP/1.1
> Host: api.addons.microsoftedge.microsoft.com
> User-Agent: curl/8.7.1
> Accept: */*
> Authorization: ApiKey ...
> X-ClientID: ...
> Content-Type: application/zip
> Content-Length: 345344
>
* upload completely sent off: 345344 bytes
< HTTP/1.1 500 Internal Server Error
< Content-Length: 0
< Strict-Transport-Security: max-age=31536000; includeSubDomains
< x-ms-middleware-request-id: ...
< Request-Context: appId=...
< Date: Tue, 04 Feb 2025 17:59:14 GMT