Account Profile Summary endpoint /profile/user/wow includes a list of the user’s WoW characters. Each character has a link to that character’s Protected Character Profile Summary at wow_accounts[i].characters[j].protected_character.href.
The link should match /profile/user/wow/protected-character/{realmId}-{characterId}, but it actually looks like https://eu.api.blizzard.com/profile/user/wow/protected-character/1306-lu?namespace=profile-eu, identical for all characters on the same realm and obviously broken. The lu in there looks like a printf-style format specifier that is missing the percent sign.