For each milestone there is a bill should be payed by the client.

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Note added at 16 mins (2023-02-10 16:42:45 GMT)
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Sorry for payed : should be paid.

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Note added at 18 mins (2023-02-10 16:45:05 GMT)
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https://milestonepay.com › article › what-is-a-milestone-payment-a-30-second-guide
What is a milestone payment? A 30 second guide | MilestonePay
Feb 8, 2022How do milestone payments work? In short, a milestone payment is when a freelancer or contractor is paid in stages of progress throughout the course of a project when agreed work is completed. The use of milestone payments usually means that a freelancer or contractor is completing what the client wants.

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Note added at 24 mins (2023-02-10 16:50:36 GMT)
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The project is divided in milestones. For each milestone there is a payment should be paid by the client. So مرحلة is of the project but not of the payment. That's way I say : مستحقات المرحلة رقم واحد
another option
دفعة المرحلة الاولى