Xdebug

Install xdebug for version

apt-get install php7.4-xdebug

then edit the config file

vim /etc/php/7.4/fpm/conf.d/20-xdebug.ini

Values to be like

zend_extension=xdebug.so
xdebug.mode=trace
xdebug.output_dir=/srv/trace

Then in the code put in

xdebug_start_trace();

make it up locked , then run the code and monitor the trace ( vim no wrap helps - :set nowrap )