Generally speaking, if your diamond ring invoice is lost, you can still take it to the store to exchange it. However, the specific exchange policy may vary from store to store. Some stores may require you to provide invoices or other supporting documents at the time of purchase to prove that you are the legal owner of the diamond ring. If you lose your invoice, you can try to contact the store to see if there is any other way to prove that you bought a diamond ring.

In addition, if your diamond ring is customized or has special properties, the store may make different provisions on the exchange policy. In this case, you need to further communicate with the store to determine whether you can exchange money and understand the relevant policies and regulations.

In short, if you want to exchange money, you'd better contact the store that bought the diamond ring first to find out their specific exchange policies and regulations.