Http-connector payload length constrained for POST request

when trying to cast payload from String to SPIN I’m getting an error:
class org.camunda.spin.impl.json.jackson.JacksonJsonNode cannot be cast to class java.lang.String (org.camunda.spin.impl.json.jackson.JacksonJsonNode is in unnamed module of loader @6536e911; java.lang.String is in module java.base of loader 'bootstrap') [ start-instance-error ]

Am I right that the payload is constrained to 4000 char length and if it’s true, is there a method to bypass this limit?