Check if the amount total is zero and in that case doesnt let you Validate de invoice.
Check and Giro module by Alphasoft.
Commission Report
Common Report Header for All Reports
Copy Invoice order Line
Automate deferred costs and revenues entries
With different cost center manage different type of costs.
Create all the moves for Cost spreading in just one click
Accounting Reports with counterpart support
Partner balance reports using payable and receivable counterparts
Apps will help to Create picking from customer invoice
Croatian Localization
OCA Financial Reports
Customer Billing for Several invoices.
Credit limit rules by amount, count of invoice and overdue
odoo app will print Customer Credit Limit Report