Format all your numbers internationally. As we send from our platform all over the world you will need the country prefix. Add the country prefix, and take off the + and the first 0 from the number.
E.g. A Dutch number: 0612345678, country prefix(+31) should be entered as: 31612345678
E.g. A UK number: 0712345678, country prefix (+44) should be entered as: 44712345678
Without the international format, you might end up sending to the wrong country!
Make sure the mobile phone numbers you enter are correct and valid. This way you won't waste balance on messages sent to non-existent phone numbers.
If you want to add the country codes to all the numbers in your excel file in one go, there is some advice on how to do this here!