It will not be possible to conduct a Home Office online right to work check in all circumstances as not all individuals will have an immigration status that can be checked online. If the online check is not possible, you should conduct the manual check.
Individuals with an eVisa, Biometric Residence Card (BRC), Biometric Residence Permit (BRP) and Frontier Worker Permit (FWP) are only able to evidence their right to work using the Home Office online service.