Fix PHP HTTP Client Error & Date Availability Bug

We need a WordPress/PHP developer to diagnose and resolve two issues on a booking site using LatePoint and Paystack. First, the dummy booking form intermittently shows no dates available even though agent schedules and matching rules are properly configured. Second, the final payment step throws a PHP SDK error: Error: No HttpClient specified for requests. You should investigate the date filtering logic, fix the missing HTTP client dependency, and verify that test bookings can be completed end-to-end. Please apply if you have experience troubleshooting WordPress plugin logic and API client issues, and can deliver a quick turnaround.