Incompatibility with Guzzle HTTP Client Versions Other Than ^7

This api client currently has a dependency on the Guzzle HTTP client, specified to be version ^7. This strict version requirement is causing incompatibility issues when attempting to use this client in environments where a different version of Guzzle is in use and required. The client should not require a specific http client. Instead, it should require a PSR-18 compliant HTTP client.