Constant BACKUP_REQUEST_MAX_PAYLOAD_SIZE_BYTES 

pub const BACKUP_REQUEST_MAX_PAYLOAD_SIZE_BYTES: usize = _; // 131_072usize

Maximum payload size of a backup request

Note: this is just a current hard limit, that could be changed in the future versions.

For comparison - at the time of writing, ecash module backup with 52 notes is around 5.1K.