Can you pay for Grab taxi in Thailand with cash?

Yes, of course you can. Immediately after installing the app and registering, this payment method will be available by default, and if you want to add a card for payment, you can do so in the account settings. But Russian cards do not work there, including UnionPay, so if you don't have a foreign card, you need to pay for the trip in cash at the end.

More details about the Grab taxi app in Thailand are described here - https://nashaplaneta.net/asia/thai/art-prilojenie-grab-uber-v-thailande

Where to go in Thailand for the first time?
Do I need a category "A" license to rent a motorbike?
Can I exchange rubles in Phuket?
Follow the link, all these questions are discussed in the chat - https://t.me/thailand_travel_chat