I have one issue with purchase return for FIFO method. I have purchase first time 5unit for 30$/unit and then I purchase second time 5units for 40$ than I return on my second purchase but it take cost 30$/unit to return so account Interim Receive will be difference with debit note. Do you have any solution for this issue?

I reviewed our Support Tickets and we are aware of this and are working on a change for a future version of Odoo. See also https://github.com/odoo/odoo/issues/45671

Thank Ray for your feedback, may I know when we can solve this issue because when user make mistake or they need to return product to supplier it really hard to do as we need to do adjustment. Otherwise when we use FIFO we dont know how to adjust cost which update wrong by return for example if we have only two transaction we can do by cost adjustment but if we have many transaction I dont know how can I update the last transaction of cost.

I face the same problem as @Theany mentioned here, Do you have a solution?

We currently support "financial fifo" and what you are asking for is a custom valuation method that supports "actual cost" which is currently solved via customization, please contact your Odoo Account Manager or your Odoo Partner to discuss if this option is right for you. Our Product Owners are aware that people have requested actual cost as a configuration option instead.