Material Group1 in VA01 Non editable

Hi Experts,

We have created a BDC For creating a sales order in VA01 but we are getting an error for material group1(WGRU1) and material group2(WGRU2) that "it is not an input field". If we create a sales order manually with reference then those fields are editable but otherwise they are coming as non editable(greyed out).

Kindly suggest a solution as entering data in those fields is the main requirement.