attaching suppliers to a draft initiative using REST API

Summary:

I am trying to attach suppliers to draft initiatives. When I am trying to process multiple number of records in a file and invoke REST API call individually for each record, the REST API is behaving in weird way. I am passing only supplier name but it is automatically taking SendSupplierQuestionnaireFlag as true.

However, when I am individually running the same paylaod, the SendSupplierQuestionnaireFlag is becoming false (which is correct).

Content (please ensure you mask any confidential information):

Payload:
{"Supplier": <Supplier_Name>}

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

REST API: https://<Oracle POD>/fscmRestApi/resources/11.13.18.05/supplierInitiatives/<InitiativeID>/child/suppliers