If you implemented a custom REST client by creating class RestClientCustom as a subclass of RestClientDefault and overriding the ajaxCall() function, then you need to update your implementation. The ajaxCall() function is now part of the RestClient interface, and its arguments are changed. See Custom REST Client to define the RestClientCustom class with the ajaxCall() function.
In addition, when you implemented your ajaxCall() function in class RestClientCustom, it used jQuery. Now inside the RestClient interface, the arguments in ajaxCall() are changed and it does not use jQuery anymore.
jQuery is no longer available in nnl_iframe.