DNS Blacklist - ionic app with httpClient.post

Good morning,

we faced some issue where we had no connection through our network to our server. The problem was, that our public ip got blacklisted and the clients (ionic 3 and ionic 4 applications) were unable to connect to the server.

Is there a way to prevent this? Do we need to implement some specific header or something?

getData<T>(postData, path): Promise<T> {
        const headers = new HttpHeaders({
            'Content-Type': 'application/json'
        return new Promise((resolve, reject) => {
            this.http.post(API + path, JSON.stringify(postData), {headers: headers})
                .subscribe(res => {
                    resolve(res as T);
                }, (err) => {