To plan payments, what matters is when the money reaches the bank. A sale today paid in 30 days can improve the month's profit and leave this week's cash untouched.
An example with numbers
You start the week with $2,000. You invoice $5,000 that you will collect next month and pay a supplier $2,700 today. With no other movements, you are $700 short when the payment is due.
Try it with your numbers
Place each movement in the week it is collected or paid. Find the first week with a shortfall and the amount you would need to cover.
Example figures for learning purposes. They are not a recommendation and do not replace professional advice.