The log-likelihood function of the TPPXG distribution is given by:
$$
\ln L(\alpha,\theta)=2n\ln \theta-n\ln(\alpha+\theta)-\left(3n+\sum_{i=1}^n x_i\right)\ln(1+\theta)+
\sum_{i=1}^n\ln \left((1+\theta)^2+\frac{\alpha \theta}{2}(x_i+1)(x_i+2)\right)
$$
References
"Wani, M. A., Ahmad, P. B., Para, B. A. and Elah, N. (2023). A new regression model for count data with applications to health care data. International Journal of Data Science and Analytics."