I have searched the whole forums and found several posts on how to do delete validated/posted invoices and none of them worked for me!!

Many have recommended cancelling only as it wont have any effect, but the thing is that all of these invoices are a TEST to test the integration and syncing with our website/app. 

Once again many recommended ( including @Ray )creating a new database, but it means that I have to hire the developer once again to repeat what he has already done or modify every syncing feature we need and reconnect it with the new database!! 

Also, we have already created and customized the whole chart of account to suit our needs, we created all the journals we need, created all of our bank accounts, our contacts, customers, vendors, employees, payrolls, etc...

We really can't just create a new database!

Anyhow, I think it is way better for me and cheaper to just delete all of these invoices and completely erase them from the existing database as there are hundreds of them generated through our testing as our business is e-commerce and there are a lot of scenarios we need to account for and test.

Please advise me with a method that WORK unlike many other posts that their methods didn't work at all or for very old versions of Odoo and I'm using Odoo v14.

Thanks a lot in advance.