Security Header Not Valid When Setting up Paypal

Paypal security header is not valid error message can be shown because of the following reasons:

• You have set up live credentials and you have turned Test mode to ON. If you want to test you need to set TEST credentials and have Paypal Sandbox Account
• You have white spaces in your credentials. Eq. api_username_1a242jdj2455 – You see how much whitespaces after the Eq.
• You put wrong API credential in wrong place ex. API Signature data you put in the API Username field inside SudoWorkspace Paypal fields.