Having international client is actually very common these days especially if you are a go getting tech savvy, digital nomad entrepreneur then no doubt you are attracting clients all over the world!! If this is you, then it is very important to detail the terms for payment and currency in the contract, this will help to mitigate any risk, set clear guidelines outlining payment terms and currency, avoid any confusion and here's the kicker, it will help your cashflow #Boom!!
Unless specifically negotiated you would generally invoice your client in your home currency. However, if you and your client have negotiated and agreed to the client paying in another currency then you would invoice your client in the currency agreed upon. So this means that you will need to ensure your accounting, invoicing system allows you to invoice your clients in their preferred currency as well as accept payments using their local currency.
The best way to get paid by your international clients is to use cloud accounting software and to integrate an international payment gateway such as PayPal, Stripe and WePay. You can create a specific online payment link and display this on your invoices so your clients can pay you online via the invoice itself via credit card or ACH (automated clearing house AKA Bank transfers) payment options. You can also request to be paid into a nominated bank account via a wire transfer simply by presenting your bank account details on the invoice.
You also want to keep in mind when setting up and using payment gateways such as Stripe, PayPal and WePay that payment processing fees are involved. You can on charge the fees to your client by adding them into the invoice totals that way you do not incur these expenses, if you do this it is important to stipulate these fees when invoicing so your client is aware.
Choosing the best method of payment instructions for your clients will be dependent on the nature and structure of your business operations as well as the location of your clients and how they can make payments and you can receive them.