statement EXECUTE isn't possible call from SPI_execute_with_args function

Hello

I can't to execure a prepared statement with one parameter via
SPI_execute_with_args function.

pavel=# select name, statement from pg_prepared_statements ;
name │ statement
──────┼────────────────────────────────
xx │ PREPARE "xx" AS select 10 + $1
(1 row)

EXECUTE "xx"($1)

ERROR: there is no parameter $1 - but function is called with one parameter

Regards

Pavel Stehule