Problem with substitution of parameters on SPI_execute_plan function in Postgresql - postgresql

Question

I'm trying to execute an SQL statement on a C core-function on Postgres. I'm using the SPI (Server Programming Interface) to do this.
The code is partially shown below.
However, when I execute the SPI_execute_plan, the argument $1 should be substituted by the parameter received on the function, but it is not being done correctly. The result is always the SPI_ERROR_ARGUMENT case.
I would like to know if I can print the SQL statement with the argument $1 substituted by the command and what is the problem with my code.
I'm using Postgres version 13.2 on CentOS 7.
Thanks in advance!
PG_FUNCTION_INFO_V1(print_statistics);
Datum print_statistics(PG_FUNCTION_ARGS) {
if (PG_ARGISNULL(0) || PG_ARGISNULL(1)|| PG_ARGISNULL(2) || PG_ARGISNULL(3)) {
ereport(ERROR, (errmsg("Null parameters are not accepted.")));
}
text *arg1 = (text *)PG_GETARG_TEXT_P(0);
char * str1 = (char *)palloc(VARSIZE_ANY_EXHDR(arg1) + VARHDRSZ);
SET_VARSIZE(str1, VARSIZE_ANY_EXHDR(arg1) + VARHDRSZ);
memcpy(str1, VARDATA_ANY(arg1), VARSIZE_ANY_EXHDR(arg1));
Oid argtypes[1] = {25};
char nulls[1] = {' '};
Datum values[1];
values[0] = CStringGetDatum(str1);
char* query = "SELECT * FROM table1 WHERE name = '$1'";
SPIPlanPtr plan = SPI_prepare(query, 1, argtypes);
elog(INFO, "arg1 (%s): %s", str1, DatumGetCString(values[0]));
SPI_connect();
int result = SPI_execute_plan(plan, values, nulls, false, 0);
switch(result){
case SPI_OK_SELECT: {elog(INFO, "SPI_OK_SELECT! Result: %d\n", result); break;}
case SPI_ERROR_ARGUMENT: {elog(INFO, "SPI_ERROR_ARGUMENT. Result: %d\n", result); break;}
case SPI_ERROR_COPY: {elog(INFO, "SPI_ERROR_COPY. Result: %d\n", result); break;}
case SPI_ERROR_OPUNKNOWN: {elog(INFO, "SPI_ERROR_OPUNKNOWN. Result: %d\n", result); break;}
case SPI_ERROR_UNCONNECTED: {elog(INFO, "SPI_ERROR_UNCONNECTED. Result: %d\n", result); break;}
}
SPI_finish();

Answer 1

The problem happened because I put the command to prepare the query before openning the connection with SPI.
The correct here is put the SPI_prepare(query, 1, argtypes); after the SPI_connect() command.