What is Bussiness Messaging Credit (Whatsapp) in Zoho CRM?

I am trying to integrate Whatsapp API into Zoho CRM. so I am reading this documentation below:

https://help.zoho.com/portal/en/kb/crm/connect-with-customers/business-messaging/articles/whatsapp-integration#Integrating_WhatsApp_Messaging_Service_with_Zoho_CRM

but I see about credits like this

I am trying to find more info about this credit but unfortunately I can't find it. I mean, I need info about what is the 'credit'? is it the same amount as the money we top up? how much credit will be deducted if I do certain actions, how much money should we pay to get certain credits, etc. is there any documentation about this?