How to convert Avro object data to Json string?

Question

Java

Hello.
Guys, this is the story.
There was a json with data and a protocol created it on the structure - generated it. Got an object.
Successfully using the ObjectMapper, the data was written to the object, now the reverse process is needed.
I also try to convert through ObjectMapper objectmapper.writeValueAsString(objectAvro).
But there are errors AvroRuntimeException trying to convert Map Schema.
Errors occur.
How to correctly convert data from avro object to json string?