Handling error messages on mobile when there are many fields

I am designing a signup form that has the following fields in it:

  • Username
  • Email
  • Password
  • Confirm Password
  • Where did you hear about us?

I have to show validation errors in these fields.

There are a couple of options in my mind:

  1. Show a tooltip on each field (Tooltip might hide other fields)
  2. Showing a popup with a summary of errors (Not a good idea)
  3. Showing placeholders in each field with examples then showing an error message on signup. (Can password fields have example placeholder?)

Any idea on how to handle this situation?

Here's the Screen:

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