Tracking remittance payments worldwide is difficult because many countries do not track funds that are sent or received. Based on data the World Bank is able to collect, a statistical model is used to estimate the amount of money coming from each sending country to each receiving country. Because these numbers are estimates, there is some room for error. For example, the total incoming or outgoing remittances displayed for some countries may not equal the actual remittances total.

https://www.pewresearch.org/global/interactives/remittance-flows-by-country/