I have currency configuration as follows

use frame_support::traits::{Currency};

and in frame config

type Currency: Currency<Self::AccountId>;

Then in an extrincis function, I am trying to do a transfer

<T as Config>::Currency::transfer(

This throws an error

     --> /home/dev/Desktop/projects/GIANT/pallets/provider/src/lib.rs:281:5
  278 |             <T as Config>::Currency::transfer(
      |             --------------------------------- arguments to this function are incorrect
  281 |                 transaction_fee,
      |                 ^^^^^^^^^^^^^^^ expected associated type, found `u128`
      = note: expected associated type `<<T as pallet::Config>::Currency as Currency<<T as frame_system::Config>::AccountId>>::Balance`
                            found type `u128`

But when I explore tests for transfer function in the substrate it uses integer values

                    <Balances as Currency<_>>::transfer(&1, &2, 3, AllowDeath),
                    Error::<$test, _>::LiquidityRestrictions

This throws an error as well

            <T as Config>::Currency::transfer(


            <T as Config>::Currency::transfer(
      |             --------------------------------- arguments to this function are incorrect
  281 |                 100,
      |                 ^^^ expected associated type, found integer

How to fix this issue?

1 Answer 1


As the error is noting, the it expects an associated type Balance, not a concrete type.

While your runtime may use the u128 type, your pallet does not know that, and instead uses a generic type which you must take into account.

The easiest thing would be to use sp_runtime::traits::UniqueSaturatedInto;, then add .unique_saturated_into() to your value.

/// Just like `From` except that if the source value is too big to fit into the destination type
/// then it'll saturate the destination.
pub trait UniqueSaturatedFrom<T: Sized>: Sized {
    /// Convert from a value of `T` into an equivalent instance of `Self`.
    fn unique_saturated_from(t: T) -> Self;

So something like this compiles:

use sp_runtime::traits::UniqueSaturatedInto;
let source = T::Lookup::lookup(source)?;
let dest = T::Lookup::lookup(dest)?;
<Self as Currency<_>>::transfer(

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