sharepoint online – newform.aspx Source= URL has query parameters with &


Currently, I have a filtered SP page with parameters (FilterField1=Title&FilterValue1=XXX). Adding a new item to the NewForm.aspx – My Source url is Source=xxxxx.sharepoint.com/process/SitePages/Plan.aspx?FilterField1=Title&FilterValue1=customer%27s%20TradeShow%20-%2020

After I hit Save the Redirect removes the & and everything after it, so returns this- xxxxxx.sharepoint.com/process/SitePages/Plan.aspx?FilterField1=Title

I want to have the redirect keep the parameters so the plan page is filtered again.

How can I all the parameters to stay in the source redirect?