Why am I being asked to grant access to my clients in order for them to fill out the form? This is for my customer registration form

Hi,

Could you let us know on which form is this happening on?

It most likely sounds like the form is set to private, which is why your clients will need to ask for access to the form.
Could you kindly check for form access settings, and set the form to public?
Guide: How-to-change-the-access-settings-of-a-form

If that would not help, could you kindly give us a link to the form, so that we can check further?