Throughout this and other repos here .block() is used excessively. Should n't it be dropped (e.g. it seems that nio 4 does not support calling it).

So the next code:

    @Override
    public Flux<User> getUsers(Mono<Integer> limit) {

        return WebClient
                .create(api_url)
                .get()
                .uri(uriBuilder -> uriBuilder.queryParam("limit", limit.block()).build())
                .accept(MediaType.APPLICATION_JSON)
                .exchange()
                .flatMap(resp -> resp.bodyToMono(UserData.class))
                .flatMapIterable(UserData::getData);
    }

should be rewritten into more non-blocking style:

    public Flux<User> getUsers(Mono<Integer> limit) {
        return limit
                .map(l -> UriComponentsBuilder
                            .fromUriString(api_url)
                            .queryParam("limit", l).toUriString()
                )
                .map(urlString -> WebClient.create(urlString))
                .map(WebClient::get)
                .map(spec -> spec.accept(MediaType.APPLICATION_JSON))
                .flatMap(WebClient.RequestHeadersSpec::exchange)
                .flatMap(resp -> resp.bodyToMono(UserData.class))
                .flatMapIterable(UserData::getData);
    }

http://apifaketory.com/api/user?limit=10 is no longer available.

I am using http://private-anon-ce456ed119-apifaketory.apiary-mock.com/api/user?limit=1
as an interim solution. However, it returns only 1 user regardless of limit param

when mapping between json format and Card object, the expiration_date field is null, it is not mapped correctly, to map it you have to add the @JsonProperty ("expiration_date") annotation in the Card class and the same annotation on the getter and setter, also you have to do the same thing for the timezoneType field in the ExpirationDate class

Whitelabel Error Page
This application has no configured error view, so you are seeing this as a fallback.

Tue Sep 03 17:20:45 PDT 2019
There was an unexpected error (type=Internal Server Error, status=500).
block()/blockFirst()/blockLast() are blocking, which is not supported in thread reactor-http-nio-4

It seems that here, standard subscription mechanism should be used instead of manually calling .block