Not 100% sure about Java SDK, but JavaScript SDK allows to specify `"now"` as a cursor to be notified of payments happening starting from when this script runs.

**Edit:**

Looks like the method mentioned above doesn't work with Java SDK. The alternative approach requires two calls instead of one, but it was battle-tested and guaranteed to work. 

Prepare request builder for transactions, set `limit` to 1 and execute it. Once you get the response, you have a `paging_token` for the first transaction in a list that can be specified as a `cursor` in streaming mode. If the first request returns zero rows, it means that there were no transactions on this account and you can safely omit a `cursor` in a streaming request call.