Is there anything I can do to get this credits accepted?

TheDude: Adding "Detective" to character names is not necessary, even though characters on other shows, or other characters on the same show, may have that title listed in their character names.

As stated at https://help.imdb.com/article/contribution/filmography-credits/characters/GKLQVXKH7U8DATWX#:

Avoid extra embellishments/repetitions/nicknames unless they are part of the credited character name: it's enough to list Robert Patrick as John Doggett in the "X-Files" TV series, instead of "Special Agent Jonathan Jay 'John' Doggett"; Jeri Ryan played Seven of Nine on "Star Trek: Voyager", not "Seven of Nine, Tertiary Adjunct of Unimatrix 01, aka Annika Hansen"; Edward Norton played Will Graham in Red Dragon, not "William Graham" or "Special Agent Graham" or "FBI Special Agent William 'Will' Graham"; Matt LeBlanc plays Joey Tribbiani in "Friends", not "Joseph 'Joey' Francis Tribbiani". You get the idea.

Admittedly, some character names with titles have been accepted in the past. But as long as the existing character name has a first name and a last name, that's good enough. IMDb is not looking to have "Detective" added to those names.