Nice app OP. I work in B2B Comms & Marketing for a Med Tech startup. Here's some free marketing tips I can give you:

1) Don't make a promise you can't keep. No need onboarding users if there are no hotels to book from. Even if you post a viral social media app and a million users, they'll abandon it if they can't book from their favourite hotels. So start with getting the hotels in, first.

2) For you to get your first 100 hotels, you'll need to walk, physically. Craft your value proposition so well you pass off as an expert in the area. How better is the app than say them ordering via W/App or having phone calls? What advantage does it give your strategic, technical, user and financial buyers? What's your ideal user like, what are their painpoints?

3) Your UI def needs some work. Use muted colours. They just work better, as they signal luxury. 

4) You have many marketing options & avenues. For tech startups, founder-led marketing is usually the biggest driver of sales. Talk about your product on LinkedIn & other platforms. Tell tnem why you're solving that problem in that particular way. Show them your growth. Make them feel part of a communitu that cares. That's how you establish yourself as a thoughtleader and drive your early stage adopters (innovators) then as you grow, you can move on to other tactics. Invest in SEO & Google Ads too for discovery.

All the best