This section describes the most common problems that customers report, and how they can be resolved:

There is a blank page when I have navigate to the Catalog > Feeds

You probably don't have the required library zf1/zend-reflection.

Solution: Please, try to install the library through composer:
composer require "zf1/zend-reflection"

I have added a category filter by fews categories,

but my feed doesn't contain any products

Such troubles usually occur when you use the "CATEGORY IS 1,2,3,4..." condition. This means that only products assigned to ALL of those categories simultaneously will be exported in the feed.

Solution: Try to change the condition to the "CATEGORY IS ONE OF..." instead, and regenerate the feed.

A required attribute is missing or incorrect [price]

Try adding a currency directly to the price attribute from the content settings of the feed, and regenerate it.

Before: <g:price>{{ product.final_price }}</g:price>
After: <g:price>{{ product.final_price }} EUR</g:price>

Also, you can define the currency directly in the Google Merchant Center: image

Two out of three attributes are missing [GTIN, Brand, MPN]

It happens when gtin and brand attributes are not provided. Try creating a dynamic attribute with the following statements:
image and use it in the <g:identifier_exists> tag.

Here is an example of how you can use it in the feed: image