How to increase maximum POST variable on Directadmin

My Software is RVsitebuilder are integrated with Directadmin.
It has a problem, When submit POST large data, it shows the error log by the following

System::load_to_env: loading variable 'POST' is larger than MAX_ENV_LEN(125749) so will be skipped

How to increase and adjust MAX_ENV_LEN? Which configuration file?

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