NPGSQL SELECT FROM dblink issue - database

Question

I have created a Blazor application with .Net6 framework. This application is generating multiple threads to transfer data from multiple PostgreSQL databases (tenant) to a single PostgreSQL database (group) using dblink.
DBLink group-tenant connections "reporting_cn_salesinvoicing{x}" have been created at the moment of the database creation.
For example if the group has three tenants, it also has three dblink servers:
reporting_lk_salesinvoicing1
reporting_lk_salesinvoicing2
reporting_lk_salesinvoicing3
And also has three dblink connections:
reporting_cn_salesinvoicing1
reporting_cn_salesinvoicing2
reporting_cn_salesinvoicing3
DBLink connections are being checked every time before a command is executed using the following command:
SELECT dblink_connect('reporting_cn_salesinvoicing{0}', 'reporting_lk_salesinvoicing{0}')
Each thread is operating a foreach loop for every table transfer with the following command:
INSERT INTO public."sales_document_line" ("tenantx_id", "id", "sales_header_id", "description", "quantity", "amount") SELECT 1, "id", "sales_header_id", "description", "quantity", "amount" FROM dblink('reporting_cn_salesinvoicing{x}', 'SELECT {x}, "id", "sales_header_id", "description", "quantity", "amount" FROM public."sales_document_line" ') AS rt(id uuid, sales_header_id uuid, description text, quantity numeric, amount numeric) ON CONFLICT ("tenantx_id", "id") DO UPDATE SET "sales_header_id" = excluded."sales_header_id", "description" = excluded."description", "quantity" = excluded."quantity", "amount" = excluded."amount"
If the above query is executed in parallel for different tenant databases usually it throws the following error:
On Postgres11
2F003: password is required
DETAIL: Non-superusers must provide a password in the connection string.
On Postgres14
08001: could not establish connection
DETAIL: missing "=" after "reporting_cn_salesinvoicing{x}" in connection info string
While some other time it exposés:
'An exception has been raised that is likely due to a transient failure.'
This error seems misleading to me because if there is only one thread is working.
I have tried to set lot of different connection parameters or changes the threading population without success.
UPDATE
After lot of hours, seems that even with parallel connections if the credentials are specified on the dblink instead of named connnetion it works:
INSERT INTO public."sales_document_line" ("tenantx_id", "id", "sales_header_id", "description", "quantity", "amount") SELECT {x}, "id", "sales_header_id", "description", "quantity", "amount" FROM dblink('dbname=salesinvoicing-qa{x} port=5432 host=xxxxxxxxxxx user=postgres password=xxxxxxxxxxxx', 'SELECT "id", "sales_header_id", "description", "quantity", "amount" FROM public."sales_document_line" ') AS rt(id uuid, sales_header_id uuid, description text, quantity numeric, amount numeric) ON CONFLICT("tenantx_id", "id") DO UPDATE SET "sales_header_id" = excluded."sales_header_id", "description" = excluded."description", "quantity" = excluded."quantity", "amount" = excluded."amount";
Any ideas?