Samsung g920t imei repair error.

So my problem is that the other day a client brought me his phone its a g920t s6 from t-mobile. The phone came with a damaged IMEI, i tried flashing a cert with Octoplus, z3x and chimera and every time i got an error… Octoplus marks that my security is damaged and Z3x has an error at RIL checking or something like that… I dont have the backups of this phone. I tried flashing some backups from my own phone with no success…
So is there a way to fix this issue.?