Bank Transfer
Using Mail In Payment as a gateway will give you a text area to enter payment details for the client. This can be used to enter the bank routing code (sometimes called sortcode) and account numbers and any references required to allocate the payment correctly.
When you receive the payment, you would need to add the transaction manually into WHMCS by using the Add Payment section of the invoice.
Server Modules
cPanel/WHM - DirectAdmin - Plesk - Helm 3 - Helm 4 - Ensim - InterWorx - WebsitePanel - Cloudmin
Lxadmin - Virtualmin Pro - XPanel - HyperVM - SolusVM - Cloudmin - WHMSonic - VPS.Net
CentovaCast - SCPanel - MediaCP - GameCP - TCAdmin - Reseller Central - Auto Release - Heart Internet
Registrar Modules
Enom - ResellerClub - Nominet - OpenSRS - ResellOne - OnlineNIC - PlanetDomain - Affordable Domains
TPP Wholesale - TPPInternet - Stargate - Namecheap - NetEarthOne - Bizcn - InternetBS - GMO Internet
12Register - Registercom - DotDNS - WebNIC - Dot.TK - HexoNet - Realtime Register - Registereu
RRPProxy - ResellerCamp - TransIP - Heart Internet - IPMirror - NetRegistry - OVH - VentraIP Wholesale
Email - 101Domain
Fraud Modules
MaxMind - VariLogiX FraudCall - Telesign
Gateway Modules
2CheckOut - AsiaPay - Auth.net Echeck - Authorize.net - Authorize.net CIM - Bank Transfer - BidPay
BluePay - BluePay Echeck - BluePay Remote - Boleto - CashU - CC Avenue - ChronoPay - Direct Debit
EMatters - E-Path - eProcessingNetwork - eWAY Tokens - F2B - Finansbank - GarantiBank - Gate2Shop
Inpay - InternetSecure - IP.Pay - Kuveytturk - Modulo Moip - Mail In Payment - Merchant Partners
Merchant Warrior - IDEALMollie - Moneris - Moneris Vault - Skrill 1-Tap - NaviGate - NETbilling
Netregistry Pay - NoChex - Offline Credit Card - Optimal Payments - PagSeguro - Payflow Pro - Pay Junction
Paymate AU and NZ - Payment Express - PayPal - PayPal Card Payments - PayPal Express Checkout
PayPal Payments - PayPal Payments Pro - PayPoint.net (SecPay) - Payson - Planet Authorize - ProtX VSP Form
PSIGate - Quantum Gateway - Quantum Vault - SagePay - SagePay Tokens v2 - SecurePay
SecurePay AU - Secure Trading - TrustCommerce - USA ePay - WorldPay - WorldPay Invisible