Text to Talk on Kindle App won’t work on some Bluetooth speakers.

When connecting to some Bluetooth speakers with either the iPad or iPhone they will play music or regular audiobooks; however when trying to use the accessibility feature to do text to talk on the Kindle app it will not play through the Bluetooth speakers only through the iPad or iPhone built in speakers. It works on my car Bluetooth but not portable speakers. Not sure how to get this to work. I tried both JBL and Sony portable speakers and have the same issue.