If you are unable to request payment after completing a collaboration, it means the brand handles their payments internally so they had to disabled their payment request feature and will pay you upon the agreed date.

I recommend messaging the brand letting them know your approved content has been posted on your social channel. From there, they would let you know how they handle their own payment processes. 

Additional Resources/Related Articles:

Outline of All Types of Payment

How do Payments Work?

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