You want create a price at service level,
this functionality is not available, see Q5 in OSS note 499626 - FAQ: BAPIs in the service procurement
you did not make use of PO_PRICE field in POITEM sturcture, this means that SAP is searching for a price and does only take the price from your BAPI if it cannot find a price itself, see OSS note 580225 - Purchasing BAPIs: Conditions and pricing
and I cannot see the field BPUEB in your data. Sometimes initial is not equal to space, I would add it and submit space as value (dont forget the X in X-structure)