CREATE TYPE testdto AS (
	id int4,
	loc geometry,
	description varchar(100));

CREATE TABLE public.test (
	id int4 NULL,
	loc geometry(POINT) NULL,
	description varchar(100) NULL
);

public class TestDto
    {
        [PgName("id")]
        public int Id { get; set; }
        
        [PgName("description")]
        public string Description { get; set; }

        [PgName("loc")]
        public Point Location { get; set; }
    }

CREATE OR REPLACE PROCEDURE public.sync_test(parameters testdto[])
 LANGUAGE plpgsql
AS $procedure$  
BEGIN
 INSERT INTO test
 select * FROM UNNEST(parameters::testdto[]);    
END; 
$procedure$
;

            var par1 = new TestDto
            {
                Id = 1,
                Location = new NetTopologySuite.Geometries.Point(-25.551136, -49.1929618) { SRID = 31983 },
                Description = "test 1"
            };
            var par2 = new TestDto
            {
                Id = 2,
                Location = new NetTopologySuite.Geometries.Point(-25.551136, -49.1929618) { SRID = 31983 },
                Description = "test 2"
            };

            List<TestDto> l = new List<TestDto>();
            l.Add(par1);
            l.Add(par2);

            NpgsqlConnection connection = new NpgsqlConnection(_connectionString);
            try
            {
                connection.Open();
                connection.TypeMapper.MapComposite<TestDto>("testdto");
                connection.TypeMapper.UseNetTopologySuite();
                NpgsqlCommand command = new NpgsqlCommand("", connection);
                command.CommandText = "CALL sync_test(@parameters)";
                var cmdParam1 = command.CreateParameter();
                cmdParam1.ParameterName = "parameters";
                cmdParam1.Value = l;
                cmdParam1.DataTypeName = "testdto[]";
                command.Parameters.Add(cmdParam1);
                command.ExecuteNonQuery();

            }            
            catch (Exception e)
            {
                _log.LogError(" Error:{error}" + e.ToString());
                throw;
            }
            finally
            {
                connection.Close();
            }

Exception message:  System.Exception: 'While trying to write an array, one of its elements failed validation. You may be trying to mix types in a non-generic IList, or to write a jagged array.'

System.Exception
  HResult=0x80131500
  Message=While trying to write an array, one of its elements failed validation. You may be trying to mix types in a non-generic IList, or to write a jagged array.
  Source=Npgsql
  StackTrace:
   em Npgsql.Internal.TypeHandlers.ArrayHandler`1.ValidateAndGetLengthNonGeneric(ICollection value, NpgsqlLengthCache& lengthCache)
   em Npgsql.Internal.TypeHandlers.ArrayHandler`1.ValidateAndGetLength(Object value, NpgsqlLengthCache& lengthCache)
   em Npgsql.Internal.TypeHandlers.ArrayHandler`1.ValidateObjectAndGetLength(Object value, NpgsqlLengthCache& lengthCache, NpgsqlParameter parameter)
   em Npgsql.NpgsqlParameter.ValidateAndGetLength()
   em Npgsql.NpgsqlParameterCollection.ValidateAndBind(ConnectorTypeMapper typeMapper)
   em Npgsql.NpgsqlCommand.<ExecuteReader>d__116.MoveNext()
   em System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   em Npgsql.NpgsqlCommand.<ExecuteReader>d__116.MoveNext()
   em System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   em System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   em System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   em Npgsql.NpgsqlCommand.<ExecuteNonQuery>d__104.MoveNext()
   em System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   em System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   em System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   em System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   em Npgsql.NpgsqlCommand.ExecuteNonQuery()


  Esta exceção foi gerada originalmente nesta pilha de chamadas:
    Npgsql.Internal.TypeHandlers.UnknownTypeHandler.ValidateObjectAndGetLength(object, ref Npgsql.Internal.TypeHandling.NpgsqlLengthCache, Npgsql.NpgsqlParameter)
    Npgsql.Internal.TypeHandlers.ArrayHandler<TElement>.ValidateAndGetLengthNonGeneric(System.Collections.ICollection, ref Npgsql.Internal.TypeHandling.NpgsqlLengthCache)

Exceção interna 1:
InvalidCastException: Can't convert .NET type 'DapperAcessLibrary.DTO.TestDto' to PostgreSQL '.<unknown>' within an array