string limitation for payload sent as input to CPQ REST API

Dear Team,

Please help with the below query we are having.
Is there any way we can store data(json format) in files or other format for 20 million plus characters and fetching data in BML script( the data is coming from an interface appication)?
We are checking this because we are getting error while encoding a data having 20 million plus characters and stroring in a variable in json and passing the json as a string to API as an input.