API Integration Inquiry: Order Injection for Lightspeed K-Series

Hello Deliverect Team,
My name is Yoav, and I am the lead developer for a restaurant based in Amsterdam.
We currently use the Lightspeed Restaurant (K-Series) POS system. I am building a custom mobile app to handle our online ordering, and we need a reliable way to "inject" these external orders directly into our Lightspeed register and kitchen workflow.
Since we are looking to use Deliverect as the bridge between our app and the POS, I have a few questions regarding your Channel API:

Process: What are the steps to get API credentials for a custom-built ordering application?
Environment: Do you provide a sandbox/staging environment for testing order flows before going live at the restaurant?
Requirements: As the merchant owner is already using Lightspeed, what specific Deliverect plan or "add-on" is required to enable custom API access?
I look forward to hearing from you so we can get this integration started.
Best regards,
Yoav Elem