Hi, Mahalakshmi!
"It's not getting loaded" means that itab is empty after SELECT statement? Or you get a short dump?
If it is empty, you can go to SE16 and copypaste VBELN to check whether you have corresponding entries in your mandant. If entries are found, please check the type of P_sales (maybe wrong length and leading zeros).
If you get a short dump, please check the definition of it_vbak (number, type and order of fields) because you are using INTO TABLE addition.
Besides that I hope that there are checks that it_vbak (it_ekko) is not initial before selecting for all entries from VBAP and KNA1 (EKPO) and you just omitted them.
So, please add some info for the community to be able to help you.