Activate the developer mode. Go to Settings> technical >Sequences & identifiers>Sequences search for invoice and edit the records

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Hi Carol Leaman,

Follow these steps to activate developer mode.: Go to Settings-->Technical -->Sequence and Identifiers -->Sequence -->Select the model.

You can change the sequence here.

See similar examples here: https://www.odoo.com/forum/help-1/question/how-to-change-the-quotation-order-invoice-sequence-numbers-55366

For more info, visit

https://www.odooimplementation.com/

Hi Carol Leaman,

Just the below link, it will show the detailed answer. to change the PO number, as like you can change the invoice number.

https://www.odoo.com/forum/help-1/question/how-to-customize-the-po-number-135006#answer-135268

Thanks

Hi,

Please go through 

https://www.odoo.com/forum/help-1/question/how-do-i-customize-next-invoice-number-2779

Activate the developer mode. Go to "Settings/Sequences & identifiers/Sequences" and customize the sequences according to your requirements.