If you are going to Singapore just to meet the client, to discuss requirements for a project for instance, you should be able to do so with a visa.
However, as you state you are going to stay there for 30 days, I suppose you are planning to work for the customer (do actual development work) during your stay.
For this, you need a Work Pass, not a visa.
You can find more information about work passes on the Singapore Ministry of Manpower website.
The various types of passes have different eligibility requirements (like qualifications, earnings, types of jobs and industries, citizenship, quotas...). In most cases you would also be salaried, not freelancing.
We're missing a lot of information about your specific situation (including qualifications, earnings...), but it would seem to me (from 10 000 feet) that an S Pass may be the most appropriate. There's a self-assessment tool available to check if you are eligible.