linux - Why chmod gives "Operation not permitted" error?

I try to execute chmod on a file with Termux, but it sends back an error which I'm unable to solve.
My phone is not rooted. If you can help me I would be most grateful to you for this! Here is the command and the error:

$ chmod +x /sdcard/meta-install.sh
chmod: changing permissions of 'meta-install.sh': Operation not permitted

Thanks!