Instagraph Send API Empty Text error, subcode 2534052

Question

I'm developing an app using the Instagram messaging / send api and am sporadically getting this error

Request

data=f'recipient={{"id":"{reply_recipient_id}"}}&message={{"text":"{rm}"}}'
r = requests.post("https://graph.facebook.com/v20.0/me/messages?access_token={}".format(access_token), data=data)

Response

{'error': {'message': '(#100) Empty text', 'type': 'OAuthException', 'code': 100, 'error_subcode': 2534052, 'fbtrace_id': 'ABtZnf58ICsDpqWwJslG2wD'}}

Any idea on what this is?

Thanks