Problem

Using filter expression on a field returns the following error:

filters: field filter: could not check repeated value for type string

This suggests that you are using a filter expression to check for an array item on a non-repeated string field, and your filter expression might look like:

"filter": "category = ['kids']"
CODE

Note: For this example, we assume ‘category’ is a STRING field.

Solution

The syntax of filter expression for a non-repeated field is slightly different than the syntax for a repeated field (e.g. List of Strings).

The syntax for a filter expression for a non-repeated field should be:

"filter": "category = 'kids'"
CODE
Documentation

Filtering Content