Hi @jawahar ks
Per my research, I would recommend you to grant access using use SharePoint app only. Then you can get access token by the app only.
Here is the document about SharePoint app only
https://learn.microsoft.com/en-us/sharepoint/dev/solution-guidance/security-apponly-azureacs
Please refer to the following steps to get an access token
https://global-sharepoint.com/sharepoint-online/in-4-steps-access-sharepoint-online-data-using-postman-tool/
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