You can integrate the Application Insights with your Azure function for free, but there is some data limit per day that you can utilize free of cost. This Azure article will discuss how to configure application insights in Azure.
How To Enable Application Insights For Azure Functions
If you are first time configuring application insights in Azure, You can enable it by following the below steps
1. Navigate to the Azure Function App. On the Function App page, click the Application Insights link in the left navigation and then click the Turn on Application Insights button.

2. Select the Enable option under the Application Insights option.

3. Expand the Change your resource option. Unless and until you already set up an Application Insights resource for this particular app, choose the Create new resource option, and then click on the Apply button.

Once you click the Apply button, It will prompt you to the below pop-up. Click on the Yes button. Now, it will show you the changes that are applied.

Now, if you click on the Application Insights link from the left navigation again.
Now, you must select the options below based on how you want to obtain the data. Select the options below and click the Apply button to save the changes.

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Conclusion
This article discussed how to enable Application Insights for Azure Functions. Thanks for reading this article !!!

I am Rajkishore, and I have over 14 years of experience in Microsoft Azure and AWS, with good experience in Azure Functions, Storage, Virtual Machine, Logic Apps, PowerShell Commands, CLI Commands, Machine Learning, AI, Azure Cognitive Services, DevOps, etc. Not only that, I do have good real-time experience in designing and developing cloud-native data integrations on Azure or AWS, etc. I hope you will learn from these practical Azure tutorials. Read more.