Weak annihilation contributions
Analysis of non factorizable contributions to $D\to V\ell\ell$ is done in ( Citation: Feldmann, Mueller & al., 2017 Feldmann, T., Mueller, B. & Seidel, D. (2017). $D \to ρ,\ell^+\ell^-$ Decays in the QCD Factorization Approach. https://doi.org/10.1007/JHEP08(2017)105 ) . There are also comments on transfering the results to $D\to P\ell\ell$.