HttpMessageNotReadableException: JSON parse error / Required request body is missing

entity.parse.failed API Error: Malformed JSON in request body (entity.parse.failed / JSON parse error) InvalidDefinitionException com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class X and no properties discovered is an invalid start of a value System.Text.Json: '<' is an invalid start of a value. Path: $ | LineNumber: 0 | BytePositionInLine: 0 json_decode null json_decode() returns null / JSON_ERROR_SYNTAX: Syntax error JSONDecodeError json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0) MethodArgumentNotValidException MethodArgumentNotValidException: Validation failed for argument [0] MismatchedInputException com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize value of type `java.util.ArrayList` from Object value not JSON serializable TypeError: Object of type datetime is not JSON serializable Port 8080 in use Web server failed to start. Port 8080 was already in use. The JSON value could not be converted System.Text.Json.JsonException: The JSON value could not be converted to System.Int32. Path: $.id Unexpected character encountered while parsing value Newtonsoft.Json.JsonReaderException: Unexpected character encountered while parsing value: <. Path '', line 0, position 0 UnrecognizedPropertyException com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "x", not marked as ignorable UnsatisfiedDependencyException UnsatisfiedDependencyException / NoSuchBeanDefinitionException: No qualifying bean of type 'X' available Whitelabel Error Page Whitelabel Error Page — This application has no explicit mapping for /error