Revenue Recognition field is greyed out in item category

Hi  Experts,

We are implementing new sales processes for a customer who is already using Revenue Recognition process. But when I tried to create a new item category or copy the existing item category, the field is greyed out.

I also tried the configuration path:-Spro - Sales and Distribution - Basic functions - Account assignment/Costing - Revenue Recognition - Set Revenue recognition for item categories. But the same issue, the field is greyed out.

Please provide your valuable input. Thank you.

Regards,

S.Vivek