Cannot Change Source Agreement number in PO Line

Summary:

Say I have 2 BPA : Same Supplier/Site/Currency/category etc. Non Item (Expense)

BPA 1 with 100$ Agreed amount and BPA2 - 200$

Create a req against BPA1 for 150$ - Autocreate to PO

PO is in Incomplete Status as 150$ exceeds the BPA1 agreed amount.

Issue : I go to PO Line > Try to change the Source Agreement to BPA2 but I don't see anything in that LOV

Expense PO

Same req BU

Same Supplier/Site/Currency across BPA/Req/PO.

Content (please ensure you mask any confidential information):

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):