Clear Cache of Samsung Pay app. & Restart your Handset..If still issue Continue then take Backup & do Factory Resetting and while Accepting terms & Conditions during Factory Resetting don't accept All, Check one by one and disable box of Marketing & Promotion wherever you got..Since I am using this App from Nov.'17 Onwards & have not received even a single Ads..
you are using some third party app which is giving you such advertisement issues. Check in device care which app is consuming more battery. Take a backup on smartswitch "BUT NOT THE APPS, ONLY CONTACTS, PHOTOS, VIDEOS, DOCUMENTS". Download the apps from playstore after reset and samsung cloud if you are using it. Do a factory reset which will take around 30 mins. I assure you samsung never promotes advertisements in its apps, its not like MI where in the MIUI itself you get advertisement. If your problem is solved then please select 3 dots on my first comment and click "Accept Solution".