Missouri State Self Employed Unpaid Sales Tax

in 2017 i ran a small side business selling bitcoin on a 3rd party marketplace xcoins.io.  Both my business as well as xcoins.io are now defunct.  I received payments through PayPal.  I filed with Turbotax and imported my P/L from Quickbooks Online Self-Employed.  I purchased audit insurance with Turbotax.

 

I received a letter in November from Missouri DOR saying I owe unpaid sales tax on my sales in 2017.  I have sent the report showing at transaction level detail that all of my sales were made through xcoins.io. 

 

I am currently waiting on their response but is there anything else that I can do?  Is there anyone else that can help me?  I don't know what section of Turbotax to even look for this help.  I have been stressing about this $30k tax bill that I can't pay and would appreciate any help that I can get to solve this situation.