Just done my TM30 myself at Jomtien but with all correct paperwork from condo landlord. Slightly confusing at first in immigration because of amount of people there but not too bad. Took me 1
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hour start to finish. Make sure you have copies of all relevant info asked for. Check on Google.
Without knowing why void was stamped not a question that can be answered as immigration will have same info on their screen when you arrive for visa exempt or on arrival.
If its of interest in addition to my comment above,i checked my new and old passport today and in 25 years and 41 entries to Thailand not once have I been asked on entry about my finances. But many times have obtained visa in u.k. before arriving.