Hi
After i add custom fields and put them Layout position "ontop" productdetail page does not work,"500 - flexv2_customfields not found"
how to fix this error?

Give me more info.

What custom field type you are using?
Why are you choosing "ontop"?
Did you try to create "Specifications" TAB?
What Virtuemart version you are using?

If your intention is to create "Specifications" TAB as explained in the TUTORIAL.PDF; your Custom Fields types MUST BE "String" (don't use any other custom field beside "String")

Another solution you can try (this works in most cases when customFields file yields not-found error message)

1- Rename these file
/templates/YOUR_TEMPLATE/html/com_virtuemart/productdetails/default.php
/templates/YOUR_TEMPLATE/html/com_virtuemart/productdetails/default.xml
to
/templates/YOUR_TEMPLATE/html/com_virtuemart/productdetails/default2.php
/templates/YOUR_TEMPLATE/html/com_virtuemart/productdetails/default2.xml


and
/templates/YOUR_TEMPLATE/html/com_virtuemart/productdetails/flexv2.php
/templates/YOUR_TEMPLATE/html/com_virtuemart/productdetails/flexv2.xml
to
/templates/YOUR_TEMPLATE/html/com_virtuemart/productdetails/default.php
/templates/YOUR_TEMPLATE/html/com_virtuemart/productdetails/default.xml


then, choose the "default layout" through VM Backend Configuration (instead of flexv2 layout). This time the Virtuemart will try to find the default_customfields.php, and you won't end up with not-found-error.

Regards.

The first problem "ask a question" tab not working at all
The main problem is that when you create custom fields and publish them in position "ontop" productdetail page not working, error 500 - Layout flexv2_customfields not found.
My test site ru-russia.ru
login in a Private Message

According to the tutorial, if I create a custom field and put it in position ontop should appear tab "specification". In this case, I have a 500 error.
Tab "ask a question" just does not appear.
I tried to rename the files as you wrote, but no change

The solution is;

1- See the attached ZIP file.

2- UNZIP it and you will get this PHP file: default_customfields.php
3- then, upload it to here:
/templates/YOUR_TEMPLATE/html/com_virtuemart/productdetails/default_customfields.php

the problem will be gone.

FYI: I have already took care the patch on your website. The "Specification" Tab works just fine on this product: ru-russia.ru/wc/wc-melnica-79-detail

I am providing the solution only for helping for those who experience the same problem.

Regards

Thank U.
Tab "specification" works. But there was a problem with the tab and the link, "Ask a question" - they did not appear. In the plugin settings they are enabled.
How to solve this problem?

Navigate to; Virtuemart Backend >> Configuration >> Shopfront
and enable this option: "Allows to Ask a question"

then they should start being displayed.

regards.