Cannot get transfer entrypoint

Question

I'm trying to call an FA1.2 transfer function from another contract. Here is my endpoint in the FA1.2 contract:

type action is
| Transfer of michelson_pair(address, "from", michelson_pair(address, "to", nat, "value"), "")
...


function main (const p : action ; const s : storage) : (list(operation) * storage) is
block {
   if amount =/= 0tz then failwith ("This contract does not accept tezi deposits"); else skip;
  } with case p of
  | Transfer(n) -> ((nil : list(operation)), transfer(n.0, n.1.0, n.1.1, s))
  | Approve(n) -> ((nil : list(operation)), approve(n.0, n.1, s))
  | GetBalance(n) -> (get_balance(n.0, n.1, s), s)
  | GetAllowance(n) -> (get_allowance(n.0.0, n.0.1, n.1, s), s)
  | GetTotalSupply(n) -> (get_total_supply(n.1, s), s)
end

Here is how I try to call the contract. I define a type to call it:

type transfer_action is Transfer of michelson_pair(address, "from", michelson_pair(address, "to", nat, "value"), "")

and I try to get the entrypoint like this:

const token_contract: contract(transfer_action) = case (Tezos.get_entrypoint_opt("%transfer", storage.token_address): option(contract(transfer_action))) of
  | Some (c) -> c
  | None -> (failwith("incorrect contract") : contract(transfer_action))
end;

The call always fails with "incorrect contract". Calling GetBalance for example works, but Approve and Transfer do not. I also tried "%transfer" and "%Transfer".

Answer 1

So I figured out a solution, I don't know why this works but it does (or why it doesn't work without the solution).

The contract I'm trying to trigger transfers from is an FA2 token contract. I need to define the transfer_action type before I import the fa2 type declarations

type transfer_action is TransferAction of michelson_pair(address, "from", michelson_pair(address, "to", nat, "value"), "")

#include "../../../partials/fa2/fa2_types.ligo"

inside the types declaration file I define the type to call the balance_of function:

type balance_of_request is record
    owner: token_owner;
    token_id: token_id;
end;

type balance_of_request_michelson is michelson_pair_right_comb(balance_of_request);

for whatever reason the balance_of_request_michelson type declaration makes the fetching of the transfer entrypoint fail. If anyone knows why that happens, please share.