Legal Question in Intellectual Property in California

That depends on the nature of your work agreement that you entered with the app developer. Your contract should state when the developer is paid and what he has to do to be paid, among other related details. Without seeing the contract, there is really no way for me to determine who should get paid when.

If there was no contract signed, then your obligation to pay and his obligation to work would be based on circumstantial evidence that you have not provided in your question.

If you and the developer cannot agree on who "puts up" first, it would be a good idea to contact an escrow agent, an attorney in California who deals with these matters, or to consider filing in small claims court.