Getting "HTTP/1.1 100 Continue" as response while trying to create a Item Invoice

Hi, I am getting "HTTP/1.1 100 Continue" as response while trying to create a Item Invoice, it will be helpful if you can let me know why I am getting this error and how to fix.

REQUEST:

{
"Number": "IT0033",
"Date": "2019-04-05",
"Customer": {
"UID": "94dcxxxx-3cxx-48cx-bxxc-02caxxxxe83"
},
"Lines": [{
"Type": "Transaction",
"Description": "Bookkeeping",
"ShipQuantity": "1",
"DiscountPercent": 0,
"Total": 200,
"Item": {
"UID": "10fxxxxa-6xx8-4xxx-9xxe-952axxxx586fa"
},
"TaxCode": {
"UID": "632axxxx-bxex0-4xx0-a2xx-7xxxx7c8a09"
}
}, {
"Type": "Transaction",
"Description": "Tax Preparation",
"ShipQuantity": "1",
"DiscountPercent": 0,
"Total": 200,
"Item": {
"UID": "826a1ea4-b053-45d1-9b59-602525ac3cf8"
},
"TaxCode": {
"UID": "632axxxx-bxex0-4xx0-a2xx-7xxxx7c8a09"
}
}, {
"Type": "Transaction",
"Description": "Payroll",
"ShipQuantity": "1",
"DiscountPercent": 0,
"Total": 75,
"Item": {
"UID": "4b9xxxx-9xxx-4xxx-8xxb-425exxxx2ca8"
},
"TaxCode": {
"UID": "632axxxx-bxex0-4xx0-a2xx-7xxxx7c8a09"
}
}, {
"Type": "Transaction",
"Description": "Quarterly BAS Prep",
"ShipQuantity": "1",
"DiscountPercent": 0,
"Total": 50,
"Item": {
"UID": "f150xxxx-axxd-4xxx-bxxa-45xxxxb543e"
},
"TaxCode": {
"UID": "632axxxx-bxex0-4xx0-a2xx-7xxxx7c8a09"
}
}, {
"Type": "Transaction",
"Description": "Financial Statement Preparatio",
"ShipQuantity": "1",
"DiscountPercent": 0,
"Total": 50,
"Item": {
"UID": "4b9xxxx-9xxx-4xxx-8xxb-425exxxx2ca8"
},
"TaxCode": {
"UID": "632axxxx-bxex0-4xx0-a2xx-7xxxx7c8a09"
}
}, {
"Type": "Transaction",
"Description": "Year-end Payment Summaries",
"ShipQuantity": "1",
"DiscountPercent": 0,
"Total": 75,
"Item": {
"UID": "8e2xxxb8-dxxx-4xxx-9xx7-f9xxxxd63c4f"
},
"TaxCode": {
"UID": "632axxxx-bxex0-4xx0-a2xx-7xxxx7c8a09"
}
}, {
"Type": "Transaction",
"Description": "Superion Lodgs",
"ShipQuantity": "1",
"DiscountPercent": 0,
"Total": 75,
"Item": {
"UID": "7edxxxxf-xxx5-4xxx-axx2-e1edbxxxxx67"
},
"TaxCode": {
"UID": "632axxxx-bxex0-4xx0-a2xx-7xxxx7c8a09"
}
}, {
"Type": "Transaction",
"Description": "Annual Statement",
"ShipQuantity": "1",
"DiscountPercent": 0,
"Total": 50,
"Item": {
"UID": "219xxxxe-axxx-4xxx-8bxx-cf99xxxxx330"
},
"TaxCode": {
"UID": "632axxxx-bxex0-4xx0-a2xx-7xxxx7c8a09"
}
}],
"IsTaxInclusive": true,
"Subtotal": 775,
"TotalTax": 70.47,
"TotalAmount": "775",
"JournalMemo": "Auth Code: 413812\nTrace ID: 20080xxxx19948\n"
}

RESPONSE HEADERS:

Array([http_code] => HTTP / 1.1 100 Continue)

Thanks