Example Caldera Forms processor classes. See: https://calderaforms.com/doc/creating-caldera-forms-processors-using-caldera_forms_processor_processor-class/

apex-processor-pre.php

<?php
/**
* Example Caldera Forms Processor Class
*/

class CF_Apex_Processor extends Caldera_Forms_Processor_Processor {

	/**
	 *  Pre-process callback
	 *
	 * @param array $config Processor config
	 * @param array $form Form config
	 * @param string $proccesid Process ID
	 *
	 * @return array|null
	 */
	public function pre_processor( array $config, array $form, $proccesid ){
		//Setup $this->data_object
		$this->set_data_object_initial( $config, $form );

		//Get errors and return if there are any
		//At this point errors would be beacuse of missing requirments
		$errors = $this->data_object->get_errors();
		if ( ! empty( $errors ) ) {
			return $errors;
		}

		//Get all processor field values as an array
		$values = $this->data_object->get_values();

		//Get one field's values
		//First argument is processor field ID
		//Second argument is default. This is optional. The default default is null.
		$customer_id = $this->data_object->get_value( 'customer_id', 42 );

		//You can add errors
		$this->data_object->add_error( __( 'This is sub apex', 'text-domain' ) );


		//Before ending this method, store the processor data in the transient
		$this->setup_transata( $proccesid );

		//Don't return anything if there are no errors!

	}

	/**
	 *  Process callback
	 *
	 * @param array $config Processor config
	 * @param array $form Form config
	 * @param string $proccesid Process ID
	 *
	 * @return array
	 */
	public function processor( array $config, array $form, $proccesid ){
		// TODO: Implement processor() method.
		// NOTE: Doing anything with this method is totally optional, but you must define this method.
	}
}

example-mailing-list-processor.php

<?php
/**
 * Example Caldera Forms mailing list processor
 */
class CF_MailingList_Processor extends Caldera_Forms_Processor_Newsletter {

	/**
	 *  Pre-process callback
	 *
	 * @param array $config Processor config
	 * @param array $form Form config
	 * @param string $proccesid Process ID
	 *
	 * @return array|null
	 */
	public function pre_processor( array $config, array $form, $proccesid ){
		//Setup $this->data_object
		$this->set_data_object_initial( $config, $form );

		//Get errors and return if there are any
		$errors = $this->data_object->get_errors();
		if ( ! empty( $errors ) ) {
			return $errors;
		}

		$result = $this->subscribe( array(
			'email' => $this->data_object->get_value( 'email' ),
		), $this->data_object->get_value( 'list' ) );

		//all is good, record and return nothing
		if( true === $result ){
			//Before ending this method, store the processor data in the transient
			$this->setup_transata( $proccesid );
			return;
		}

		//set and return errors
		$this->data_object->add_error( $result );
		return $this->data_object->get_errors();

	}

	/**
	 * Add the newsletter client here
	 *
	 * @param $client
	 */
	public function set_client( $client ){
		$this->client = $client;
	}

	public function subscribe( array $subscriber_data, $list_name ){
		//This is super-psuedocode :)
		return $this->client->subscribe( $subscriber_data, $list_name );
	}

	/**
	 *  Process callback
	 *
	 * @param array $config Processor config
	 * @param array $form Form config
	 * @param string $proccesid Process ID
	 *
	 * @return array
	 */
	public function processor( array $config, array $form, $proccesid ){
		// TODO: Implement processor() method.
		// NOTE: Doing anything with this method is totally optional, but you must define this method.
	}
	
}

example-payment-processor.php

<?php
/**
 * Example Caldera Forms Payment Processor
 */
class CF_Pay_Processor extends Caldera_Forms_Processor_Payment {

	/**
	 *  Pre-process callback
	 *
	 * @param array $config Processor config
	 * @param array $form Form config
	 * @param string $proccesid Process ID
	 *
	 * @return array|null
	 */
	public function pre_processor( array $config, array $form, $proccesid ){
		//Setup $this->data_object
		$this->set_data_object_initial( $config, $form );

		//Get errors and return if there are any
		$errors = $this->data_object->get_errors();
		if ( ! empty( $errors ) ) {
			return $errors;
		}

		//Input is valid, make payment
		//BTW I know it's silly that you have to pass arguments to this method
		$result = $this->do_payment( $config, $form, $proccesid, $this->data_object );
		//check for errors
		if( true  !== $result ){
			if( is_string( $result ) ){
				$this->data_object->add_error( $result );
			}else{
				$this->data_object->add_error( __( 'Unknown error', 'text-domain') );

			}

		}

		//Get errors and return if there are any
		$errors = $this->data_object->get_errors();
		if ( ! empty( $errors ) ) {
			return $errors;
		}

		//Before ending this method, store the processor data in the transient
		$this->setup_transata( $proccesid );

		//Don't return anything if there are no errors!

	}

	/**
	 * Do the payment
	 *
	 * @param array $config Processor config
	 * @param array $form Form config
	 * @param string $proccesid Process ID
	 * @param Caldera_Forms_Processor_Get_Data $data_object
	 *
	 * @return string|bool
	 */
	public function do_payment( array $config, array $form, $proccesid, Caldera_Forms_Processor_Get_Data $data_object ){
		$api_key = $this->data_object->get_value( 'api_key' );
		$amount = $this->data_object->get_value( 'amount' );
		$response = wp_remote_post( 'https://apexpay.com/api/payment', array(
			'body' => array(
				'key' => $api_key,
				'ammount' => $amount
			)
		));
		if( ! is_wp_error( $response ) &&  200 == wp_remote_retrieve_response_code( $response ) ){
			return true;
		}elseif ( is_wp_error( $response ) ){
			return $response->get_error_message();
		}elseif ( is_array( $response ) && isset( $response[ 'error' ] ) ){
			return $response[ 'error' ];
		}else{
			return false;
		}
	}

	/**
	 *  Process callback
	 *
	 * @param array $config Processor config
	 * @param array $form Form config
	 * @param string $proccesid Process ID
	 *
	 * @return array
	 */
	public function processor( array $config, array $form, $proccesid ){
		//Get transient data back
		$this->setup_transata( $proccesid );
		$this->set_data_object_from_transdata( $proccesid );

		//save meta data in submission
		global  $transdata;
		if ( ! isset( $transdata[ $proccesid ][ 'meta' ] ) ) {
			$transdata[ $proccesid ][ 'meta' ] = array();
		}

		$transdata[ $proccesid ][ 'meta' ][ 'amount' ] = $this->data_object->get_value( 'amount' );



		return $transdata[ $proccesid ][ 'meta' ];
	}

}