ERROR: Invalid captcha value.

This worked for me to get it running again:

I had installed and activated the plugin. For tests I used current Opera Browser, WP 5.2.1
Settings:
– only for contact form 7
– OK for Enable to hide captcha for logged in users.
– OK for all mathematical operations
– display as numbers
– captcha time: 300
– OK for Block direct access to wp-comments-post.php

Tests resulted in errors although the solution was correct.

I deactivated both “Enable to hide…” and “Block direct access …” and saved settings.

Tests we running ok then.

I activated “Enable to hide…” again, saved settings: Tests we running ok
I activated “Block direct access …” again, saved settings: Tests we running ok

Finished.
I love this plugin! I even love it much more when it’s running fine! :-)

Hope it helps!