Getting error 42601 when running procedure in PostgreSQL

OpenGL

I've deleted this and created a new topic with a minimal example included.
https://forum.qt.io/topic/120460/minimal-sql-program-that-fails-what-is-wrong-with-it

I've created a program that connects to a PostgreSQL database and now I'm trying to call a procedure (that works, I've tested it directly in the database)
but this fail

QSqlQuery query(m_db);
query.prepare(QString("call add_new_task(?,?,?,?,?, ?, ?)"));
query.bindValue(0, task.get_c());
query.bindValue(1, task.get_d());
query.bindValue(2, task.get_p());
query.bindValue(3, task.get_e());
query.bindValue(4, task.get_after());
query.bindValue(5, task.get_before());
query.bindValue(6, 0, QSql::InOut);

if (query.exec())  { ... this is not run ... }
else { ... this is run ... }

and it fails with the error

QSqlError("42601", "QPSQL: Unable to create query", "ERROR:  syntax error at or near \"(\"\nLINE 1: EXECUTE  ('C X', 'D X', 5, 8, '2020-10-31', ...\n                ^\n(42601)")

In the postgresql logs I see

syntaxerror at or near  "call" at character 25
PREPARE qpsqlpstmt_1 AS call add_new_task($1, $2, $3, $4, $5, $6, $7)
ERROR:  syntaxerror at or  near "(" vid tecken 10
STATEMENT:  EXECUTE  ('Caption X', 'Description X', 5, 8, '2020-10-31', '2120-10-31', 0)

How can I find the error? Please help me, I'm stuck.