Calculation of Long Range Interaction Energy with no cut-off

GROMACS version:2019.6
I want to calculate long range Coulombic interactions between Protein and LIgand with no cut offs in the mdp file. I switched off all cutoffs, did the rerun calculations on the trajectory using one MPI process to prevent Domain Decomposition but got the following error:

Fatal error:
Failed to allocate memory for 300124320 interactions, which is larger than the
maximum of 268435455. If your simulation is not using interaction cutoffs, you
should use them.

Please help. I am unable to proceed. Eagerly waiting for a response.