1. Login to GST Portal

  2. Click on Profile Name and select 'My Profile' from dropdown

  3. Under Quick Links, click on 'Manage API Access'

  4. Select Yes to enable API Access for your GSTIN

  5. Select the desired duration from drop-down - 6 hrs, 12 hrs, 7 days, 30 days

  6. Click on Confirm

Read step-wise process - GST Portal : Manage API Access