So it looks like the Admin UI will give an error if a higher severity block exists for example, when trying to create a lower severity block for test.example, but if both have the same severity, then the block on test.example can be created, when there's already a rule covering that from example with the same severity:

@ClearlyClaire this is what I mentioned on this documentation change: mastodon/documentation#1417 (comment)

When doing a look up for the domain block, or domain federation rule, we need to be comparing the severity and the domain

iirc the behavior of the API endpoint being different from that of the admin controller is intentional, with the API being intended to be more straightforward.

But the inability to apply a stricter block on a subdomain through the API is likely not intended, and it sounds like an unnecessary limitation. I'll look into it.

On a side note, wildcards are not supported (and are unnecessary, as any domain block applies to subdomains too).

@ClearlyClaire

On a side note, wildcards are not supported (and are unnecessary, as any domain block applies to subdomains too).
This is necessarily only if you want to block the TLD, e.g., .cf

But some *. blocks have made it into people's blocklists.