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• Next to the Webhook you'd like to test go under the Actions column. Click the "Test Webhook" option. 
• Choose a Prospect you'd like to use for your test. The Prospect's information (standard/custom fields as tokens) will be used in the test.
• Click the Submit button.
• Results of the test will be shown at the bottom of the window, as shown in the screenshot below:

Instructions

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Instructions: Requestb.in

• Go to Requestb.in and click the green button that looks like the one below. Requestb.in is a free tool to test Webhook calls. Check “Private” if you don’t want anyone else to be able to see the data. 

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