yq output redirection in C using system()

[epodegrid]

I'm using yq in a C program to covert YAML to json using the command yq ea '[.]' -o=json .cache/BT_nginx-ingress.yaml > .cache/package.json. However this causes an error.

Error: write /dev/stdout: permission denied

I use system() to run the command, and while yq works from the terminal, I get an error in this case. I have tried using yq to output to stdout i.e. the terminal and this works fine, even from within the C program, but redirecting the output fails. I have several other redirections in my program but this is the only case where it fails. All paths and file/directory rights are also fine. Can someone please help me with this? Thanks!