Give Display Custom Amount in first Place when Form Display type is set as button

functions.php

<?php
/**
 * Moves the custom amount to the beginning of the button.
 *
 * @param $output
 * @param $form_id
 */
function give_button_donations_custom_amount_first( $output, $form_id ) {

	$prices             = apply_filters( 'give_form_variable_prices', give_get_variable_prices( $form_id ), $form_id );
	$display_style      = give_get_meta( $form_id, '_give_display_style', true );
	$custom_amount      = give_get_meta( $form_id, '_give_custom_amount', true );
	$custom_amount_text = give_get_meta( $form_id, '_give_custom_amount_text', true );
	if ( empty( $custom_amount_text ) ) {
		$custom_amount_text = esc_html__( 'Give a Custom Amount', 'give' );
	}

	if ( 'buttons' === $display_style ) {

		$output = '<ul id="give-donation-level-button-wrap" class="give-donation-levels-wrap give-list-inline">';


		//Custom Amount.
		if ( give_is_setting_enabled( $custom_amount ) && ! empty( $custom_amount_text ) ) {
			$output .= '<li>';
			$output .= '<button type="button" data-price-id="custom" class="give-donation-level-btn give-btn give-btn-level-custom" value="custom">';
			$output .= $custom_amount_text;
			$output .= '</button>';
			$output .= '</li>';
		}

		foreach ( $prices as $price ) {
			$level_text    = apply_filters( 'give_form_level_text', ! empty( $price['_give_text'] ) ? $price['_give_text'] : give_currency_filter( give_format_amount( $price['_give_amount'], array( 'sanitize' => false ) ) ), $form_id, $price );
			$level_classes = apply_filters( 'give_form_level_classes', 'give-donation-level-btn give-btn give-btn-level-' . $price['_give_id']['level_id'] . ' ' . ( ( isset( $price['_give_default'] ) && $price['_give_default'] === 'default' ) ? 'give-default-level' : '' ), $form_id, $price );

			$output .= '<li>';
			$output .= '<button type="button" data-price-id="' . $price['_give_id']['level_id'] . '" class=" ' . $level_classes . '" value="' . give_format_amount( $price['_give_amount'], array( 'sanitize' => false ) ) . '">';
			$output .= $level_text;
			$output .= '</button>';
			$output .= '</li>';

		}
		$output .= '</ul>';

	}

	echo $output;

}

add_filter( 'give_form_level_output', 'give_button_donations_custom_amount_first', 10, 2 );

For Give Support Ticket: https://wordpress.org/support/topic/custom-amount-make-it-first-option-in-dropdown/#post-9867960