CAPTCHA won't validate

Hello everyone, I have some problems with my CAPTCHA. The image shows up, but when I validate mon Form (With Contact Form 7 3.7.2), the image never matches with what we write. I tried the rewriting thing in the wp-config (WPCF7_CAPTCHA_TMP_DIR), doesn’t work neither.

Thank you for your time.

https://ww.wp.xz.cn/plugins/really-simple-captcha/