Model/Adminhtml/Source/PaymentMode.php
public function toOptionArray() {
        return [
            [
                'value' => self::MODE_CARDS,
                'label' => __('Cards')
            ],
            [
                'value' => self::MODE_MIXED,
                'label' => __('Mixed')
            ],
            [
                'value' => self::MODE_LOCAL,
                'label' => __('Local payments')
            ] 
        ];
    }
public function toOptionArray() {
        return [
            [
                'value' => self::MODE_CARDS,
                'label' => __('Cards')
            ],
            [
                'value' => self::MODE_MIXED,
                'label' => __('Mixed')
            ],
            [
                'value' => self::MODE_LOCAL,
                'label' => __('Local payments')
            ] 
        ];
    }
public function toOptionArray ( ) { return [ [ 'value' => self :: MODE_CARDS , 'label' => __ ( 'Cards' ) ] , [ 'value' => self :: MODE_MIXED , 'label' => __ ( 'Mixed' ) ] , [ 'value' => self :: MODE_LOCAL , 'label' => __ ( 'Local payments' ) ] ] ; }
Possible payment modes

@return array
Possible payment modes