"Sorry, we could not create your Google Account." error using aliases

I'm trying to create a Google account. I'm using Simple Login aliases because I want this Google account to be temporary/disposable (to install the Mi Fitness app in an Android emulator, so that I can set the date and time on an old Mi Band, to use the Mi Band simply as a wristwatch, after which I will delete the emulator instance and the Google account).

But I keep running into this unhelpful error, "Sorry, we could not create your Google Account." None of these have worked:

• I have tried different browsers, both Firefox and Chrome.
• I have tried different machines, both Mac and Windows.
• I have tried different IP addresses, and two different ISPs.

So I suspect Google has a problem with the email aliases. One is "@slmail.me" and the other is "@<custom-name>.slmail.me"

Anybody else experienced this?