Can you check your Messaging Settings in your TextNow app to see if you have a Signature setup? If every message has those characters after the message you typed you may have a signature setup that you can remove.
You can check out this support article to edit or remove your signature: https://supportfree.textnow.com/hc/en-us/articles/204680799-How-to-Change-Your-Signature
This comes up after every text at the bottom!
If I were to message "hello" it would come up with:
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