Hi Tosin,
Thank you for the reply.

Although it is fine to do that, I will rather write a function. If you check, there are 3 things which vary field id, value and error message.

You can remove the previous code and use the following instead.

// forces user to select a specific select field value on registration page.
add_action( 'bp_signup_validate', function () {
	bd_tosin_validate_signup_field( 4448, 'I accept', 'This is a required field. You must accept.' );

	// You can uncomment the below function and specify your value. Repeat it as you need.
	// bd_tosin_validate_signup_field( 2, 'some other value', 'Your error message' );
	// bd_tosin_validate_signup_field( 2, 'some other value', 'Your error message' );

} );

/**
 * Validates BuddyPress signup field.
 *
 * Makes sure that the user entered value is same as the expected value. If not, the specified error will be shown.
 *
 * @param int $field_id
 * @param string $expected_value expected value to match.
 * @param string $error_message Error message to be shown if the values do not match.
 *
 * @return void
 */
function bd_tosin_validate_signup_field( $field_id, $expected_value, $error_message = 'Please try again, the value did not match our expectation' ) {

	if ( ! isset( $_POST[ 'field_' . $field_id ] ) ) {
		return; //should never happen if the field is marked as required.
	}

	$input_value = wp_unslash( $_POST[ 'field_' . $field_id ] );

	if ( strtolower( $expected_value ) !== strtolower( $input_value ) ) {
		buddypress()->signup->errors[ 'field_' . $field_id ] = $error_message;
	}
}

And you can use it for as many fields as you need.

Regards
Brajesh

You are welcome.