Possibly weaning. I think my red-bellied parrots started weaning around 8 weeks of age and were fully weaned by about 9-11 weeks give or take. I kept records but have no idea where they are now.
Do you have a gram scale to monitor weight? What other foods are you offering? If the baby has decreased activity level and is dropping weight quickly and not willing to eat anything then you need to get him/her to a vet.
You can offer the baby Cheerios, moistened pellets, millet spray and small pieces of fruits & veggies as weaning foods.