Embedding structs in golang gives error "unknown field"

You can't initialize the fields in the embedded type directly, but you can do it like this:

accounts[v.AccountId] = returnAccount{
    Account: Account{
        Tp:        v.Tp,
        AccountId: v.AccountId,
        Username:  v.Username,
    },
}

Or, if v is of type Account, you can just use

accounts[v.AccountId] = returnAccount{
    Account: v,
}

You are trying to initialize promoted fields which is not possible by composite literals. From Go spec:

A field or method f of an anonymous field in a struct x is called promoted if x.f is a legal selector that denotes that field or method f.

Promoted fields act like ordinary fields of a struct except that they cannot be used as field names in composite literals of the struct.

But you can access them using dot notation:

ra:= returnAccount{}
ra.Tp = acnt.Tp