Npgsql.Postgresexception: 53300: remaining Connection slots are reserved for non-replication superuser Connections

Question

I am using Dotnet Core and C# to fetch data from an API and saving to a Postgresql database.

And arrives at a certain part of the process in which this error appears:

Exception has occurred: CLR/Npgsql.Postgresexception Exception thrown: 'Npgsql.Postgresexception' in System.Private.Corelib.dll: '53300: remaining Connection slots are reserved for non-replication superuser Connections'

using IDbConnection _conn = new NpgsqlConnection(ConnectionStrings.BANCO);

try
{
  _conn.Open();

  return await _conn.QueryAsync(query);
catch (Exception ex)
{
  logger.LogError(ex.Message, ex);
}
finnaly
{
  _conn.Close();
}

I am using Npgsqlconnection with Dapper...

What causes this? I’m doing something wrong?