RESTBase goes to MW API via api.svc.eqiad.wmnet, but for requests for donate.wikimedia.org the following response is returned:

<p>This domain points to a <a href="//www.wikimedia.org">Wikimedia Foundation</a> server, but is not configured on this server.</p>

so RESTBase cannot fetch anything from MW API, which's makingg it unusable on donate.wikimedia.org. It's questionable whether it should be on that domain anyway though, but we either need to fix this or remove RB from that domain.