I have the following code which is returning an error as mentioned

public IQueryable<SplitStringResult> SplitStringToColumns(string inputString)
{
    return _gpModel.SplitStringResults.SqlQuery("SELECT * FROM dbo.SplitStringToColumns({0})", inputString).AsQueryable();
}

public List<ClientAccount> Transactions(string custId)
{
    var result = from rm in model.table1
                 join sp in model.table2 on rm.Id equals sp.Id into spJoin
                 from sp in spJoin.DefaultIfEmpty()
                 join sy in model.table3 on rm.Index equals sy.Index into syJoin
                 from sy in syJoin.DefaultIfEmpty()
                 from ssc in SplitStringToColumns(sy.TXTFIELD)
                 where rm.CUSTNMBR == custId
                 select new ClientAccount
                 {
                     InvoiceDescription = ssc.InvoiceDescription
                 };
    return result.ToList();
}

I am calling my function in linq instead of database approach. When I tired directly with FirstOrDefault() this works but with in the query