Hi @zanzaboonda,
I hope you are well today and thank you for your question.
The 10002 error is either that your API details are wrong or you have it in Sandbox mode using live API details. Or in Live mode using Sandbox API details.
Admin --> Products --> Settings --> Payments
/wp-admin/edit.php?post_type=product&page=marketpress&tab=gateways
Please double check it to know is there any extra space after your API Username / password /Signature.
Best Regards,