How to correctly call the vk_pay window in the VK chat bot for legal entities. faces?

Question

Bots

I really need help!
Made a chat bot, signed an agreement with DMR. I studied the instruction ( https://vk.com/dev/vkpay ) far and wide. I couldn't find this topic on the internet. When I click on the "pay via vk pay" button, a payment window pops up. After a moment, it changes to the "Unable to complete the operation, please try again later" window. My guess is that I didn't form the application signature correctly. But the thing is, I don't have an app. There is a community that has a chatbot. To generate a signature, you need an "secure application key" or "app secure key". Where can I get it? I have already tried to create a standalone application, follow the link ( https://vk.com/apps?act=manage), where in the information I indicated the community in which my chat bot is located. This application has the secure key I need and the application id. But that didn't fix the situation either. Maybe somehow you need to connect this application with the community?
In the code to call the button, I specify:

"action":{
"type":"vkpay",
"payload": "{\"button\": \""+"1"+"\"}",
"hash": f"aid={aid}&action=pay-to-service&amount={amnt}&merchant_id={merchant_id}&sign={sign}"
}

Is the hash well formed?
I will be grateful for your help!