Preview prorated rental cost for renting a phone number today

Returns the immediate prorated charge for renting one phone number from today through the end of the current billing cycle, plus the recurring monthly rate. Use this to show a “you’ll be charged $X today” preview before calling POST /product/rent-number.

Returns 400 if the organization doesn’t have the phone-numbers feature configured (contact support) or if the org is currently locked (e.g. unpaid invoices — call GET /product/unpaid-invoices first to check).