How to ensure I get my commission payout even after I tender my resignation

Hi all, I'm a B2B IT salesperson. We usually get our commission payouts after the project is completed and customer is invoiced and made payments.

I've closed a rather big project with about 5 digits worth or commission back in March.

Howeve, I've accepted a job offer back in mid of May. I've told my future employer to wait for me to wrap up my project so that I can get my commission payout. They're nice enough to wait for me so I will start in August.

However, now the problem is there is delay in equipment shipment and the project seems to be only able to wrap up in late July or early August. What should I do to ensure I get the full commission payout? My notice period is 1 month and I have yet to tender my resignation and I have to do so by end of June.

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Thanks in advance.