Fix JavaScript and API Issues on My Website

My live site hits a wall whenever it tries to load or save data through the REST API—everything just keeps spinning and nothing shows up. The HTML and CSS are solid, so the snag is hidden somewhere in the JavaScript logic or the API handshake... (Budget: $10 - $30 USD, Jobs: API Development, API Integration, CSS, Debugging, HTML, JavaScript, PHP, REST API, RESTful, Web Development)