Displaying reference pictures to a varying value in QField

While developing a QField project for forestry inventories, I aim at displaying botany board related to the current selected species selected in a scrolling-menu for field operator. It should be used as a reference to compare with the species suspected on the field. I followed this procedure : https://qfield.org/docs/prepare/add-1-n-pictures.html

Here is the referencing layer as a table containing pathes for the pictures related to the species named "photos_essence.csv"

Here is the referenced layer "Qfield_comptage.shp" used for digitizing.

In the project properties, i added a relation "photos_essence" between the referenced layer "Qfield_comptage.shp" and the referencing layer "photos_essence.csv". It should be linking species ("Essence") identified and the path to the pictures related to those species.

I added the relation "photos_essence" in Attribute Form of the "Qfield_comptage.shp" referenced layer.

Then I changed the widget type to attachment, linking it to the file containing the pictures

The end result gives a null value instead of displaying the pictures related to the species identified.

Do you have any insight of what i’m doing wrong ? I dont know if such a widget is conceivable.
Thank you in advance.