If you have ever created a prefilling link that involved a special character (e.g. #,@,%), you may have noticed that your prefilling link broke, or was cut off at the point of that special character.
When this happens, you may need to use something called URL encoding, which will translate that special character into a form that won't break your prefilling link.
You can use this document as a guide to create a prefilling link that utilizes URL encoding. You can view a complete list of URL encoded values for characters here.
Prefill Links with URL Encoding
In general, if everything is working as expected with your prefilling links, you most likely do not need to worry about URL encoding.
However, if you are only seeing parts of your field prefilled, or if fields are being cut off after certain values, then you probably need to use URL encoding.
For example, if you are attempting to prefill in an address field that involves a #, and it is not being prefilled as expected, then you should use URL encoding.
If you are sending out a prefilling link through a Salesforce HTML email template, then you can easily address this from within your template. If you have a field that has spaces or special characters, you could change your HTML template to look like this: