Paypal Express Sandbox mode error

Paypal Express seems to work fine in live mode, however when enabling the sandbox function the following error msg appears:
Connection failure - error code : 10002 , error message : Security header is not valid

What do I need to do to correctly enable sandbox mode?

Hello,

I just had a look on Paypal documentation, and first notice, Paypal Express is a deprecated payment method ( Paypal Express Documentation )

Next point, the difference between Sandbox and Production Mode in our plugin seems to be only the Url link to contact Paypal servers.
By the past of course this will used to work, so maybe the best move will be to Contact Paypal support to have clues if something change or worst aren't support anymore the sandbox mode (to prevent new development as it's a deprecated payment ?...).

The other possibility is that something between your website and Paypal servers make the sandbox url's request fails, but can't tell more about this.

Awaiting news from you.

Regards

Just realized that the paypal sandbox account has different credentials. With the correct ones the sandbox function works fine.