NFC tag we are testing goes to Apple Pay on my iPhone 8, instead of the URL we want.

I discovered the answer, my iPhone 8 requires an app to read NFC, otherwise it goes to Apple Wallet. My iPhone XR reads the code without an app and asks if I'd like to open the coded URL:

"iPhone Xs, iPhone Xs Max and iPhone XR include a new feature for NFC that Apple didn’t mention on stage. The new models will be able to scan NFC tags in the background. With current iPhones, users must first launch an app to enable NFC Reader mode."

more on this:

"There are some constraints to this system. Any NDEF tag is supported that ends with a URL that is registered with Apple’s Universal Link system. Background tag reading happens whilst the iPhone display is on (either on lock screen or home screen).

Background tag reading requires the device to have been unlocked at least once since it has been rebooted. It also is disabled if Apple Pay Wallet session is active, if Airplane mode is enabled, or if the camera is on."

quotes source: https://9to5mac.com/2018/09/12/iphone-xs-and-iphone-xr-can-read-nfc-tags-without-having-to-launch-an-app/