This instruction is explain how to start work with integration your payment gateway into Booking Calendar Business Small or higher versions of update 7.0 or newer, based on exist payment gateway.

Let say that your new payment gateway have name: loc_payment.

1) You need to create new folder, like this:

../{Booking Calendar Folder}/inc/gateways/loc_payment/

,
then create new PHP file with following name:

../{Booking Calendar Folder}/inc/gateways/loc_payment/wpbc-gw-loc_payment.php

2) After this you can copy/paste code from file

../{Booking Calendar Folder}/inc/gateways/stripe/wpbc-gw-stripe_v3.php

(or some other, which you better like)
into your new file, and replace in content terms like "stripe" or "STRIPE" to "loc_payment" or "LOC_PAYMENT" accordingly.

3) Then check your code relative comments in this new file and configure your payment form and settings, relative to API and help info from website of your new payment gateway.

4) Additionally you need to add one new hook for ability to load the new payment gateway

// General API for Adding new gateways:
function add_my_gateway( $gateway ){ return $gateway . ',gateway_ID'; }
add_filter( 'wpbc_gateways_original_id_list', 'add_my_gateway' );

In your case you need to have something like this:

function add_my_loc_payment( $gateway ){ return $gateway . ',loc_payment'; }
add_filter( 'wpbc_gateways_original_id_list', 'add_my_loc_payment' );

5) If your payment gateway have response functionality, then you can check this function:

function wpbc_payment_response__stripe_v3( $parsed_response ) {