When to pay gst on advance received before gst registration?

We received 50% on a project in June, when there was no GST regime. We received 25% in August, before getting GST registration. We have received GSTIN now. We'll finish the project in September and issue the tax invoice in September. That's when we'll received the balance 25% plus the GST on the whole amount. So do we need to deposit any GST before that? The advance we received was on the amount excluding GST.

Thanks.