parallel not working

Hi:
I write a  C function, the function is as follows:
create function st_geosotgrid(geom geometry, level integer) returns geosotgrid[]
immutable
strict
parallel safe
language c
as
$$
begin
-- missing source code
end;
$$;

At the same time, I set the relevant parameters:
force_parallel_mode: offmax_parallel_maintenance_workers: 4max_parallel_workers: 8max_parallel_workers_per_gather: 2max_worker_processes: 8min_parallel_index_scan_size: 64min_parallel_table_scan_size: 1024parallel_leader_participation: on
set parallel_setup_cost = 10;set parallel_tuple_cost = 0.001;

sql:
select st_geosotgrid(geom,20) from t_polygon_gis;

and the explain as follows:

Gather  (cost=10.00..5098.67 rows=200000 width=32)  Workers Planned: 2  ->  Parallel Seq Scan on t_polygon_gis  (cost=0.00..4888.67 rows=83333 width=32)

when i explain analyze ,the parallel worker is suspend:

I would like to know how can I get it to work properly？

Thank You!