To anyone that runs into this issue, I wanted to point something out about the ChangeIP DDNS script located on the wiki here.
If your password includes any of the special characters, you will need to escape them to properly authenticate as noted at Manual:Scripting#Constant_Escape_Sequences. I ran into this problem and (not being well versed with scripting) didn’t realize that you need to escape data within quotes as well.
Also, when putting in a support request to ChangeIP, in spite of the fact that the script was written by them and it indicates to email their support, they told me they refuse to assist with anything to do with RouterOS. If I had known they had changed their tune about RouterOS I would not have bought their services. Hope that helps anyone considering their services.
(If anyone from ChangeIP is reading this, I invite you to read Ticket #751911)