They make no mention of 6 months payslips in the visa portal. If you plan to work remotely from inside Thailand then workation is your only option. Soft Power DTVs don't provide permission to work remotely.
I'm guessing what they want to see is a residence certificate. Go to your local immigration office and get on, then go to a mobile provider and get a SIM registered against your passport (with receipt) then go to a bank and try again
You'll probably need a few forms. I usually just complete them in the immigration office as it only takes 10 minutes. But you'll also need a 12 month statement from your bank showing the required deposit, a letter from the bank to immigration and to update your bank book on the day you go.