Error In cascading Drop down - .Net Core 3.1, Ajax

Question

I have implemented a code for get categories based on Departments as follow 

 

1. The method to get Departments 

 

 

 

2. the view

 

 

3. Javascript Code to get categories based on department id

 

 

 4. Get sub Method

 

 

 

5. Error Occures as Undifine (If there is 3 categories for a particuler department Id that will display 3 undifines which means Value and Text is not passed from contaller.But the count is passing)

 

 

Please help me with this. I was tring to fix this for 3 days.