I develop a form where I need to add multiple items for one field (multi select) and the submit button is disabled as long as all fields are not valid.

This field needs to have 1 minimum tag to validate the form.

For other fields I have this view:

I have 3 possibilities :

• Enabled submit button all the time and when the user clicks on it, I display fields on error with theirs error message
• When the user cleans the multi select field I display the error message
• I display all the time an information message below the field which indicate the rule for this field

What is usually done for this? And maybe another idea?