The ability to have 50 characters in invoice numbers will appear in 2 forms in D365 F&O

PO Invoices

Invoices created from one or more POs can utilize this new length ability. Invoices can be created from selecting a PO and selecting Invoice on the Invoice tab on the ribbon under

Accounts payable > Purchase orders > All purchase orders

 -or-

Procurement and sourcing > Purchase orders > All purchase orders

Additionally, invoices related to POs can be created by selecting New on the ribbon under 

Accounts payable > Invoices > Pending vendor invoices

Vendor Invoice Journal

Invoices created directly in the invoice journal that are not linked to a PO also can be up to 50 characters.

Accounts payable > Invoices > Invoice journal

Reach out to Microsoft Support

Before making any changes to feature management, contact Microsoft Support and request to open the EnableEdtStringDatabaseStringLengthAttributeInComputation flight.

Why do we need to do this? 

Opening the flight will ensure that invoice numbers are not truncated during the invoicing process.

Enable the Feature

Once the flight is opened, simply navigate to the feature management workspace and enable the feature Extend the length of invoice number for vendor invoice

Thats it! You are now ready to use invoice numbers up to 50 characters.