As part of configuring Record Validation for Salesforce, you need to enable API access to your Salesforce environment; either by profile or by permission sets. You will need it when working with Record Validation!
Enable API access in Salesforce by profile
- Navigate to (Salesforce's) Setup > Users > Profiles
- Click the profile you want to update and click Edit
- Navigate to System Permissions
- Tick the API Enabled box
- Click Save
Enable API access in Salesforce by permission sets
- Navigate to (Salesforce's) Setup > Users > Permission Sets
- Select the permission set you want to update and click Edit
- Navigate to System > System Permissions
- Tick the API Enabled box
- Click Save