Custom notification ringtones
Default Notification Sound: Textra Settings > Customize Notifications > Notification Sound (select Zedge) > Select a ringtone.
Per Contact Notification Sound: Open Textra (Conversation List) > Long Press (to enter multi-select mode) choose the conversations you wish to customize > tap 3 dots (top right) > Customize > Notifications > Notification Sound (select Zedge) > Select a ringtone.