You are aware that this needs an MD5 hash, right?

Yes of course. My PW registration code is : SHA2('mypassword',256)

SHA2 is not MD5. Please check again.

Already tested with md5. But it does not work either.

My complete php code :

$user = 'user_name';
$onepass = 'mypassword';
$onepassmd5 = md5('".$onepass."') ;
$sql_update_LS = "UPDATE lime_users SET one_time_pw='".$onepassmd5."' WHERE users_name='".$user."'";
$req_update_LS = mysqli_query($connexion,$sql_update_LS) or die('Erreur SQL !
'.$sql_update_LS.'
'.mysqli_error());
header('Location: index.php/admin/authentication/login?user='.$user.'&onepass='.$onepass);

Works fine here. Did you activate one time passwords in config.php?

See https://manual.limesurvey.org/Optional_settings#Use_one_time_passwords

I wrote in config.php : $config['use_one_time_passwords'] = true;
And works not fine here...

Well, then you did it wrong.
Check out https://manual.limesurvey.org/Optional_settings#How_to_modify_optional_settings
For further discussion please use the forum. Thank you.