creating invoice is not working through Paypal REST API - php

Question

I am facing the problem to create the PayPal invoice through the REST API. I got the access token by using auth API of https://api.sandbox.paypal.com/v1/oauth2/token. I am passing the token in the HEADER to create an invoice in the create invoice API of https://api.sandbox.paypal.com/v1/invoicing/invoices/.
Header:
Below is my JSON body.
{
"merchant_info": {
"email": "krpdas-facilitator#gmail.com",
"first_name": "prabhu",
"last_name": "kr",
"business_name": "prabhu kr",
"phone": {
"country_code": "91",
"national_number": "2222233333"
},
"address": {
"line1": "xxxxxxxxxxx,xxxxxxx",
"city": "xxxxxxx",
"state": "xxxxxx",
"postal_code": "888888",
"country_code": "IN"
}
},
"billing_info": [
{
"email": "lalith-facilitator#abacies.com",
"business_name": "test facilitator",
"additional_info": "test facilitator's Test Store",
"address": {
"line1": "1 Main St",
"city": "San Jose",
"state": "CA",
"postal_code": "95131",
"country_code": "US"
}
}
],
"shipping_info": {
"first_name": "Lalith",
"last_name": "Kumar",
"address": {
"line1": "1234 Main Street",
"city": "Anytown",
"state": "CA",
"postal_code": "98765",
"country_code": "US"
}
},
"items": [
{
"name": "Zoom System wireless headphones",
"quantity": 2,
"unit_price": {
"currency": "USD",
"value": "120"
},
"tax": {
"name": "Tax",
"percent": 8
}
},
{
"name": "Bluetooth speaker",
"quantity": 1,
"unit_price": {
"currency": "USD",
"value": "145"
},
"tax": {
"name": "Tax",
"percent": 8
}
}
],
"discount": {
"percent": 1
},
"shipping_cost": {
"amount": {
"currency": "USD",
"value": "10"
}
},
"note": "Thank you for your business.",
"terms": "No refunds after 30 days."
}
I tried with changing the access token and merchant email ids. But always I am getting the same error as 401 unauthorized. I am following the documentation of https://developer.paypal.com/docs/api/invoicing/.
ERROR:
{
"name": "AUTHORIZATION_ERROR",
"message": "Authorization error occurred.",
"information_link": "https://developer.paypal.com/docs/api/invoicing/#errors",
"debug_id": "f89a30f937ced"
}
Scope:
"scope": "https://api.paypal.com/v1/payments/.*
https://uri.paypal.com/services/payments/refund
https://uri.paypal.com/services/applications/webhooks
https://uri.paypal.com/services/payments/payment/authcapture
https://uri.paypal.com/payments/payouts https://api.paypal.com/v1/vault/credit-card/.*
https://uri.paypal.com/services/disputes/read-seller
https://uri.paypal.com/services/subscriptions
https://uri.paypal.com/services/disputes/read-buyer
https://api.paypal.com/v1/vault/credit-card openid
https://uri.paypal.com/services/disputes/update-seller
https://uri.paypal.com/services/payments/realtimepayment",