Submitting Form With Bootstrap Modal Question

Unless you have some JavaScript to override and prevent the default behavior of the submit button, submitting the form results in a new page being loaded by the browser, even if it happens to be the same page. You can check for validation errors and show the modal again when the page loads.

If you are preventing the default behavior and submitting the form via AJAX, then you would just have to send back some indication that validation failed and check for that in the JavaScript code which is run to process the response. If the response indicates there were no validation errors, you close the modal, otherwise, you display the errors.

Do you have any examples? Or links

There's only one rule - please don't tell anyone to go and read the manual.  Sometimes the manual just SUCKS!