Get an Access Token - cURL

Download cURL for your environment.

Note: On Windows, use a Bash shell to make cURL calls.
Run this command, where <client_id> is your client ID and <secret> is your secret:
```
curl -v https://api.sandbox.paypal.com/v1/oauth2/token \
   -H "Accept: application/json" \
   -H "Accept-Language: en_US" \
   -u "client_id:secret" \
   -d "grant_type=client_credentials"
```
Note: If you use a command-line tool other than cURL, set the Accept header to application/x-www-form-urlencoded.

In exchange for these credentials, the PayPal authorization server returns your access token in the access_token field:
```
{
  "scope": "scope",
  "access_token": "Access-Token",
  "token_type": "Bearer",
  "app_id": "APP-80W284485P519543T",
  "expires_in": 31349,
  "nonce": "nonce"
}
```
Include this bearer token in the Authorization header with the Bearer authentication scheme in REST API calls to prove your identity and access protected resources. This sample request includes a bearer token:
```
curl -v -X GET https://api.sandbox.paypal.com/v1/invoicing/invoices?page=3&page_size=4&total_count_required=true \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer Access-Token"
```
Access tokens have a finite lifetime. The expires_in field contains the number of seconds after which the token expires. For example, an access token with an expiry value of 3600 expires in one hour from when the response was generated.

To detect when an access token expires, write code to either:
- Keep track of the expires_in value in the token response.
- Handle the HTTP 401 Unauthorized status code. The API endpoint issues this status code when it detects an expired token.
Re-use the access token until it expires. Then, get a new token.

Next, make REST API calls.