Join query with two tables

The error is in your syntax. You are doing WHERE 'sale_id' = '236', so you are comparing two different strings, and this condition will always evaluate to FALSE.

Your query should be written like this:

SELECT 
  payment_type,
  with_service_total,
  sale_nm 
FROM `ospos_sales_payments` 
INNER JOIN ospos_sales_items 
  ON ospos_sales_payments.sale_id = ospos_sales_items.sale_id 
WHERE sale_id = '236'

Also, if the sale_id field is numeric, you can compare to 236 also without using quotes.

Remove quote and add table name:

WHERE ospos_sales_payments.sale_id = '236'

or

WHERE `ospos_sales_payments`.`sale_id` = '236'