Unique ID for form fills for Facebook/Meta CAPI Integration

We're looking for a unique ID that could be generated and captured at the time of a Marketo form submission. That unique ID would be passed to Facebook via the Facebook conversion script pixel that fires when the form is submitted. The unique identifier cannot contain personally identifiable information (PII). We are integrating CAPI through Zapier.

Does anyone know how we can go about achieving this? Edit: We are open to any server-side solutions as well.