up the pay-pal advance in magento . I have fill all the credentials in magento admin . BUt when i go to frontend and click pay-pal button it gives
PayPal gateway has rejected request. Security header is not valid (#10002: Security error
i have googled a lot and found some suggestions like
Remove API Username, API Password and API Signature from Admin->configuration->Paypal->API/Integration Settings. clear cache and test again
i have tried all these but it still gives the same error.
Please suggest me what can be the issue