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Throttling allows you to limit the number of hits to an API during a given period of time, typically to protect your APIs from security attacks and your backend services from overuse, regulate traffic according to infrastructure limitations and to regulate usage for monetization. For information on different levels of throttling in WSO2 API Manager (WSO2 API-M), see Throttling tiers.

After you created, published, and subscribed to the API, let's see how the API Gateway enforces throttling and resource access policies to the API. 

1. Sign in to the API Store and select the PhoneVerification API.
   Image RemovedMake sure to subscribe to the API as mentioned in the before you begin section.

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2. Anchor
   AccessToken AccessToken

   Go to the Default Application, click the Production Keys tab and generate an access token.
   If you already have an access token for the application, you have to regenerate it after 1 hour. 
   
   Let's invoke this API. 

3. Click on the API, then go to its API Console tab and expand .
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4. Expand the GET method .
   Image RemovedGive values to the and click Try it out. Provide the required parameters and click  Try it out to Execute to invoke the API. For example,

   PhoneNumber

   E.g.

   
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   , 18006785432
   LicenseKey	Give 0 for testing purpose

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   Note the response that appears in the API Console. As we used a valid phone number in this example, the response returns as valid.
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   Image AddedNote that you subscribed to the API on the Bronze throttling tier. The Bronze tier allows you to make a 1000 calls to the API per minute. If you exceed your quota, you get a throttling error as shown below.
   
   Let's try to invoke the API using an unavailable resource name.

5. Go to the API's Overview page in the API Store and get the API's URL.
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6. Install cURL or any other REST client.

7. Go to the command-line invoke the API using the following cURL command. 

   Localtabgroup

   Localtab active true id Format title Format Code Block curl -k -H "Authorization :Bearer <access -token -in -step -3>" '<API's URL in step 9>/CheckPhoneNum?PhoneNumber=18006785432&LicenseKey=0' 5>/<API's-resource-name>?<parameter1>=<parameter1-value>&<parameter2>=<parameter2-value>' Localtab id Command title Command Note that the PhoneVerification API's resource name is  CheckPhoneNumber , but we use an undefined resource name as  CheckPhoneNum . Here's an example: Code Block curl -k -H "Authorization :Bearer 63cc9779d6557f4346a9a28b5cfd8b53" 'https://localhost:8243/phoneverify/1.0.0/CheckPhoneNum?PhoneNumber=18006785432&LicenseKey=0'

   Note that

   the

   the call gets blocked by the API Gateway with a 'no matching resource' message. It doesn't reach your backend services as you are trying to access a REST resource that is not defined for the API.

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   Code Block
   curl -k -H "Authorization :Bearer 344fd2a7-ee69-311a-9711-0437b0021415" 'https://localhost:8243/phoneverify/1.0.0/CheckPhoneNum?PhoneNumber=18006785432&LicenseKey=0' <am:fault xmlns:am="http://wso2.org/apimanager"><am:code>404</am:code><am:type>Status report</am:type><am:message>Runtime Error</am:message><am:description>No matching resource found for given API Request</am:description></am:fault>

You have seen how the API Gateway enforces throttling and resource access policies for APIs.