I am one of the freelancers who use your website for 1-2 years now.
That is a fantastic website in comparison with other platforms. Let me tell you my story so it might make sense.
I went on holiday and it was so hard for me to manage existing clients and apply for new projects. Yes, your site is mobile friendly but I got my message through my phone (Gmail app) and every time, I open it, it asked me for user/pass. Consider I have been there 4-5 days and I log in around 200 times. Of course, I didn't apply for many opportunities as it was so hard.
You can imagine how hard is it.
I am 100% agree with this post from 2016 (2 years ago) and some others as well
Such an app can make the life of freelancer and employer much easier and cause a lot of money for PPH site (by more collaboration happening on the site)
We have developed a similar Android app for a website (a company with the same platform in another country) and it includes all the functionalities required in a different language. It just needs to be adjust based on your needs and we can offer a very good price for it (comparing to building it from scratch). The app is containing all functionalities required such as send/receive the message, build a new project, collaborate on existing project desk, payments and many more. The platform is including 80K projects and 250K freelancer so quite large one and fully tested. I have used it for 6+ months myself.
Please think about this opportunity as a business case which improves the life of your clients (customer satisfaction) and brings more money in the long term.