I Don't think that he does not want to pay – because his major part of the business depends on that application I created and manage for him.
So my ask is to use a tactic that makes him pay on time without creating bad impression for either of us.
You have the potential leverage of an active relationship, where you do work they need for an important application, and thus have joint and mutual interests to continue on a active and healthy mutually agreeable basis.
Through all of your DAILY actions and communications directly with the person who makes the decision to pay, you are able to be devoted to re-establishing the healthy mutual interest of your client towards you. It's a person-to-person relationship, and it is a person's decision to pay you, and to maintain the relationship with you on acceptable terms. Talk to them on the telephone; email reminders are not enough.
Your repeated and daily, person-to-person statement of expectation and requirement that the client respect the relationship, and the reciprocity of the relationship, and your terms may be successful. Ultimately, if you are not important to them, they are not important to you.
One perspective: let them practice, for a week or two via these daily personal communications, where the daily opportunity to make good on the commitment and recognition of your importance, whether in daily partial payments, or a payment in full is a daily decision on their part that you are in active and personal communication about.
Eventually comes the point of time, after this ragular and daily communication, and the daily decisions on their part, for you to make clear that no work will be done until the invoice is brought up to date, and paid in full, and furthermore, that all future work will be conducted on a different basis that you establish that does not allow any payments to be delayed in any instance, as the client has demonstrated by action, and daily decisions, that you are not important to them. Invite them to commit to your being important to them.
But he still wastes your time. There's nothing wrong in walking away from a business if the terms do not suit you. On time payment is just another clause in the contract, I expect it to be honoured.
