Pricing not happening for all the pricing and item combination through API

Hi Team

I have created a function with calls Pricing API QP_PREQ_PUB.PRICE_REQUEST.

For some reason, this pricing works for few of the customer with price list and item id combination while it doesn't work for few of them.

The same works when line is entered from front end.

Please guide what could be the problem.

Thanks

Mirza Tanzeel