PayPal Error Code: 10002 Security header is not valid

PayPal error 10002 means that your API credentials are incorrect. Under Sliced Invoices -> Payment settings, double check that your PayPal API Username, PayPal API Password, and PayPal Signature are all correct.

It could be something as simple as an extra space at the end… it’s easy to accidentally copy and paste some extra white space into the field without realizing.

Also make sure you are using the “NVP (SOAP)” API keys, and not any other of the APIs that PayPal offers.