many. From financial statements (certificate from my bank saying that I mantain an average balance of X for the past 3 months), to portfolio of services, websites, podcasts, customer references, etc... showing my activity as a keynote speaker and writer... certificate from Spanish ministry of labour my last 3 months of self-employed taxes fully paid, to proof of residence in Spain (property of my own).
my case is complex as I got Business in LATAM and Europe, my tax residence for 2025 will continue to be Spain (I did not manage to spend more than 183 days anywhere else this year). My advice: talk to international tax experts
in most major cities in Thailand Internet should not be a problem. I am talking Chiang Mai, Phuket, Bangkok, Pattaya, Udon Thani, Hua Hin. Maybe in some Islands the infraestructures are less developed, but in general, you will be fine