Suggestion:
1) Firstly, user have to complete the Sales Return for wrongly selected channel partner.
2) After that do the normal channel partner, use the open PO of correct supplier.
3) User should do the Sales order and despatch, Invoice and Purchase receipt.
Note:
1) If the customer is a channel partner. user needs to select the channel partner field as ‘Yes’ in customer master.
2) If the supplier is a channel partner. user needs to select the channel partner field as ‘Yes’ in supplier master.
3) User needs to select the channel partner field as ‘Yes’ in Site Customer and Site Supplier also.
( The channel partners are business houses who does business exclusive for the organisation or a representative of the organisation for some purpose. For example an organisation who is a dealer and works as joint venture or consignment stock agent.)