Error 500 when registering with Captcha

[AnSit]

I enabled the use of Captcha (Google) in the VM options during registration. If during the registration I don't check the option "I'm not a robot", then an error 500 occurs. And there should be just a message on the page that I didn't fill in the Captcha field.
On another site, too, is a blank page and error 0.

What is the problem? How to fix it?

[jenkinhill]

What exactly is the 500 error? Turn on VMdebug.

[AnSit]

I turned on VMdebag.
No errors are output, as there is a redirection to a new page where error.php works. And there on the empty page the following error is indicated:
0 - Empty CAPTCHA is not valid.

But this error should be displayed on the registration page. Otherwise, the user needs to go back and re-enter the data. At least the password.

[GJC Web Design]

and turn on Joomla debug as well to see the call stack
check your network console tab to see the server url & response

[AnSit]

Turned on the display of all errors in Joomla. Anyway, no errors and no additional entries appeared at all.

P.S. Redirection occurs on the page: /profile/edit?limit=200&start=0

[GJC Web Design]

of course there is an error logged somewhere.. unless u can find it no one can help u

[AnSit]

I myself would be very glad to find it, but I do not find it anywhere. I will look further.

Well, well, what happens when you register with the VM, if you do not pass the spam test in captcha(Google)?

[Jörgen]

Nothing, that is the whole purpose, You have to pass

Search Your error logs for the errror condition.

Jörgen @ Kreativ Fotografi

[AnSit]

I have already reviewed all the error logs known to me! I find nothing out of error about this and at this time. 

Another important detail! If I disable registration through VM and I register simply in Joomla and do not pass the spam check through the captcha, then there are no errors (500 or 0) and there are no redirects. Just at the top of the page displays a standard message that I did not pass the test for spam.
Such incidents occur only when I turn on registration through VM.

J 3.9.0, VM 3.4.2

[Milbo]

looks like you do not load the js validator. check your browser console for js errors.

[AnSit]

Checked. Java scripts are all allowed. In the browser console there are no errors about this.