Fixed it for you using a Text Aggregator.
Basically build a JSON containing an array of the items,
Then wrap it in array brackets [ ]
Blueprint
blueprint.json (21.6 KB)
Resulting request body:
{
"items": [
{
"member_id": "MY7225565",
"invoice_number": "HQ00724755"
},
{
"member_id": "MY7195312",
"invoice_number": "HQ00724754"
},
{
"member_id": "MY2488594",
"invoice_number": "HQ00724753"
},
{
"member_id": "MY1601246",
"invoice_number": "HQ00724749"
},
{
"member_id": "MY9814255",
"invoice_number": "HQ00724751"
},
{
"member_id": "MY3161976",
"invoice_number": "HQ00724750"
},
{
"member_id": "MY1358914",
"invoice_number": "HQ00724524"
}
]
}