Create a Default value for Buyer in OMFI and choose the Indicator B for Purchase order and then assign the Parameter EVO with the created value in the user master and run one cycle.
Please go through the below link.
Please define condition control at plant level, path
Purchasing IMG, under Conditions -> Define Condition Control at Plant Level.
In purchase order, item detail, material data, please ensure that info update is ticked on
Below are its implications which are displayed with F1 help
Info record update
Determines whether the prices and conditions of this purchase order item are suggested in future PO items.
Selecting InfoUpdate causes one of the following situations to occur:
1. If just one info record (with or without plant) exists, it is updated.
2. If no info record exists and "plant condition requirement" was specified in Customizing, an info record with plant is created. Otherwise, an info record without plant is created.
3. If two info records exist (that is, one info record with plant and one without plant) the info record with plant is updated.
You can specify that prices and conditions in purchasing info records are only allowed at plant level in the Purchasing IMG, under Conditions -> Define Condition Control at Plant Level.
Hope this helps