...
API Username: format is username@company_id, provide user access via: Admin Center >> Manage Permission Roles >> Manage Integration Tools >> Enable Allow Admin to Access OData API through Basic Authentication. OnRamp requires access to these entities: User, UserAccount, EmpJob, EmpEmployment, EmpEmploymentTermination, PerPerson, PerEmail. See this link for instructions on finding your Company ID.
API Password: <api user’s password>
OAuth:
Create key pair using openssl command described here - create certificate. Use Copy the public and private keys from this step in OnRamp.
Register OAuth2 client application - register application. Use Copy the API Key from app registration in OnRamp.
Company ID - see this link for instructions on finding your Company ID.
User ID - user id of a technical user who has the right permissions to access OData API
...