You might be using an outdated version of the Samsung Wallet.
The issue might be with the payment terminal.
The card info might be incorrect.
It might not be supported in your region yet.
You might have not set up Samsung Pay Properly.
These are the usual issues
We understand your concern about Samsung Pay app, kindly try to contact us through our support channels; Live Chat, or WhatsApp for better assistance, as we need more information.
Please visit the website through the below link, go to Support, then Contact, and we will assist you further with your inquiry.