If you are searching for older orders, you may use the following link:
https://www.gunbroker.com/order?orderid=00000000
You will replace the 00000000 with your order number.
You must be logged into your account. You will be able to see the order, select the Print button in the top right corner, and print the invoice. Below is an example*:
Please be sure to print all invoices and keep them for your records to avoid this in the future.
If you do not have your order number, you find it by requesting a Transaction History Report using the GunBroker report generator: Buying History Report / Selling History Report
*This can be applied to both orders purchased and sold.