Always Encrypted Data Validation

Just a question in how could i validate duplicate data's in my database if columns is set to be encrypted(deterministic) in db? I've tried running the following code, but receive the error below.

declare '@test1' varchar(max) = 'XXXXXX'
select * from testing where t1 = '@test1'

> Encryption scheme mismatch for columns/variables '@test1'. The > encryption scheme for the columns/variables is (encryption_type = > 'PLAINTEXT') and the expression near line '4' expects it to be > (encryption_type = 'DETERMINISTIC', encryption_algorithm_name = > 'AEAD_AXS_XXX_CBA_HMAC_SHA_XXX', column_encryption_key_name = > 'CEK_Auto1', column_encryption_key_database_name = 'XXX') (or weaker). How can I find the source of this error, or is there another way to determine duplicate rows?