How do I activate custom notification ringtones on Apple Watch SE?

As a recent Apple Watch SE purchaser, I have selected several optional notification ringtones as provided by Apple. They were entered in both my watch and phone. However, they are not operative, as I still hear the single 'ding' when a message (mail or text) arrives. I have double-checked my desired tones on both the phone and watch, and they are the same, so there is no conflict. Any suggestions for my finding a way to make these new sounds active would be appreciated as I do need to have different sounds for different functions. Thank you.

[Re-Titled by Moderator]

Original Title: Notification alerts