How to Enable API Access in Salesforce
First navigate to Setup Menu
In the left-hand menu scroll to Administration > Users > Select Profiles
Select Edit next to the Profile you want to enable API Access for
Navigate to Administrative Permissions by scrolling down to System
Click on System Permissions
Hit Edit, which is in the middle of the screen
On the next page you will notice the API Enabled Checkbox
If not checked already, check and save and you are good to go
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