Send an invoice, generating a purchase from billing template data.

post https://gate.reviopay.com/api/v1/billing_templates/{id}/send_invoice/

Use this request with a BillingTemplate having is_subscription == false. Specify the BillingTemplateClient data (only client_id field is needed) in the request body. The request will issue a Purchase by combining data of BillingTemplate.purchase and BillingTemplateClient.client and will send an invoice to your Client. Response will contain data of a created Purchase. The BillingTemplateClient will not be saved.