How to fix “FFmpeg command cannot work when multip

Question

I am using FFmpeg in my php yii2 project. FFmpeg working fine in my project but one major problem is execute FFmpeg command with multiple input file. When i try to use single file to process in ffmpeg command then it works. so, how can i fix this problem? I am using hostGator shared plan for my project. Please, help if is there any process limit or file open limit on server that i don't know.

I have tried using this command in php exec():

ffmpeg -y -i /uploads/ac/10122018-09351115-a94rlvlawvikskb4vdrca.mp3 -i /uploads/ac/09012019-035928988-assknyrk8oujccwevir7.mp3 -f lavfi -i anullsrc -filter_complex "[2]atrim=duration=3[g0];[2]atrim=duration=1[g1];[2]atrim=duration=5[g2];[g0][0][g1][1][g2]concat=n=5:v=0:a=1" /uploads/jm/concat.mp3 2>&1

Above command works local side but not working on server side.

output on server side with error code 1:
Press [q] to stop, [?] for help
pthread_create failed: Resource temporarily unavailable. Try to increase `ulimit -v` or decrease `ulimit -s`.
Conversion failed!

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ulimit -v
unlimited

ulimit -s
15240