Make Supplier field readonly using Page Composer in edit PO page for negotiated PO

Summary: We need to make the supplier field read only if user is trying to edit a PO which is created from negotiation (i.e. solicitation)

Content (please ensure you mask any confidential information): We tried to achieve this using page composer. In the expression editor, I could see an binding parameter called NegotiationHeaderID. We tried using this parameter in the condition, but it is not working.

The EL expression which we wrote is as following:

#{bindings.ChangeOrderFlag.inputValue == 'Y' || bindings.IsSupplierReadOnly.inputValue || (bindings.NegotiationHeaderId.inputValue != null && bindings.NegotiationHeaderId.inputValue != '')}

Anyone has any idea on this?

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