Purchase Info record Error

Dear Experts,

I am trying to create PIR in testing server, but at the time of creation I am facing error.

Field "Valid To" next to Net price is been in grey mode and also it has been marked as mandatory field. Since it is in grey mode

I could not insert date and it is mandatory I could not save PIIR.

Please help me to find out how to change Field from mandatory to optional and from grey to input.

I have check screen layout option from SPRO, but does not help me out.

Thanks in advance.