The reason for this error is because you're not authorised on CorpPass to submit the employment income. Do follow the following steps to proceed with tax filing via API submission:
Step 1: Go to corppass.gov.sg
Step 2: Login as a CorpPass Admin
Step 3: Click on e-service access
Step 4: Click on assign selected e-services
Step 5: Select the authoriser name
Step 6: Search for Submission of Employment Income Records
Step 7: Select role: Approver, Key in Authorisation Effective Date: Date as of start of today
Step 8: Click Next.
Final step! Go back to Payboy and submit again.
For more information for tax filing, please click on this link: https://support.payboy.biz/en/articles/2575855-tax-filing