Hi,

Given that the journal belongs to the branch company, switching to the main company's journal allows the invoice to post, and manual journal entries work fine under the branch, the issue is likely specific to the Sales Invoice creation process within the branch company's context. This suggests a deeper configuration problem related to how Sales Invoices are handled in the branch company.

The problem might stem from a misconfiguration in the default accounts used specifically for Sales Invoices within the branch company's settings. Even though the journal itself is correctly assigned, the system might be pulling default accounts from the main company during the Sales Invoice creation. Check the default accounts set in the Sales app configuration for the branch company. Also, review any settings related to accounts receivable or income accounts that might be specific to Sales Invoices.

Another potential cause could be related to how Odoo determines the company context during Sales Invoice creation. There might be a rule or setting that is incorrectly assigning the main company's context to the Sales Invoice, even though the journal is correctly set to the branch company. Examine any automation rules or server actions that might be affecting the company context during Sales Invoice creation.

Hope it helps

All relevant accounts have been checked and are assigned to the main company, except for the invoice journal, which is assigned to the branch.