What to do with this Gaussian Convergence error?

Hi! I'm kind of a beginner with computational chemistry and I\m trying to study the interaction between copper ion and a graphitic carbon nitride quantum dot. the calculation converges with HF but when I try using DFT the software keeps showing me these messages

EnCoef did 100 forward-backward iterations gaussian

EnCoef did100 forward-backward iterations gaussian

EnCoef did 80 forward-backward iterations gaussian

rare condition: small coef for last iteration: -0.433d-15

and repeats

I tried different functionals with different basis sets but didn't work for me

any help?