@Rtconner: Hi, how is this website related to Wikimedia? Where to find its user data policy or privacy policy?
I am unsure if this use is in scope for https://meta.wikimedia.org/wiki/OAuth_app_guidelines and https://foundation.wikimedia.org/wiki/Policy:Wikimedia_Foundation_API_Usage_Guidelines if there was no relation to Wikimedia (and likely the docs could be clearer about that).
From looking at https://zeto.zip/login, I assume that Wikimedia is one of the available authentication options?
Also, how many requests do you expect?

Probably you are not setting a sensible user agent and so the requests get throttled aggressively. See https://foundation.wikimedia.org/wiki/Policy:Wikimedia_Foundation_User-Agent_Policy

In T417854#11630850, @Aklapper wrote:

I am unsure if this use is in scope for https://meta.wikimedia.org/wiki/OAuth_app_guidelines and https://foundation.wikimedia.org/wiki/Policy:Wikimedia_Foundation_API_Usage_Guidelines if there was no relation to Wikimedia (and likely the docs could be clearer about that).

For sure, it's an OAuth app registered on Meta-Wiki, and it makes requests to Wikimedia APIs.

Turns out this was all caused by the other issue : https://phabricator.wikimedia.org/T417839

Sorry. This can be closed. I will also add better User-Agent per the docs also.