external service array list error request body

I'm creating an external service for add value on a google sheet.

I find the error but i cannot solve it!

The request body need an array of array of string and i cannot set the values for array with apex variable

When I create the apex variable in my flow for my body request i don't find the class with body!

this is the class autogenerated

here i don't find my class but only OUT, i try to uncheck "allow multiple values" too

list of class:

If i try to create a new external service with different body in the example request, i find the class for the body but i cannot assign value into array,because google wait for array of array of string

{values:["test"]}

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