During the last couple years, opening a business bank account in HK has become increasingly difficult. Now, only certain banks will actually do this in practice.
To your question, business proof would be items like supplier and purchase contracts, business plan, etc. Anything that can substantiate your business as actively trading and ‘lower-risk’ in the eyes of the bank’s compliance department.
However, since you state that you have payment from ad networks - the nature of your business is likely as an online affiliate. Most Hong Kong banks would classify this as higher risk, more so with a seychelles company. Worse case scenario, you open the SY company and then cannot open the bank account in Hong Kong.
Your better bet would be to open a Hong Kong company OR to search for a bank account elsewhere. For instance I could set you up with a first tier bank in Singapore with a Seychelles company.
There is a list of different options to incorporate here: Incorporations.io that we made for this exact purpose, to help entrepreneurs decide on the best place to incorporate by comparing different options side by side.