How convert Date variable format in bash

I have bash variable named date_export that have 2021-09-22 as a value.
I want assign it to other bash variable named DATE_EXPORT but having other format 20210922
I tried :

DATE_EXPORT=$(date -d ${date_export} + '%Y%m%d')

But, it does not work, any help, please

>Solution :

The output format is a single word starting with +, not two separate arguments + and the format.

DATE_EXPORT=$(date -d "$date_export" +"%Y%m%d")