What is the reason why the word "may" appears before Apple's SMS number?

This is the international telephone area code.

International telephone area code, that is, the code assigned by the International Telecommunication Union to a country or special administrative region according to E. 164 standard I, all numbers are prefix numbers, that is, these numbers are used to "dial" the destination country or special administrative region. Each country also has a prefix "dial-out" country. This prefix is called the international crown code.

Extended data:

The international area code +8 is not a complete code. The international area code +8 is a country, region or system in Zone 8.

+8 1 stands for Japan, +82 stands for Korea, +84 stands for Viet Nam, +850 stands for North Korea, +852 stands for China and Hongkong, +853 stands for China and Macau, +855 stands for Cambodia, +856 stands for Laos and +86 stands for China.

+870 stands for INMARSAT“SNAC "satellite phone, +878 stands for global personal communication service, +880 stands for Bangladeshi, +88 1 stands for mobile satellite system, +882 stands for international network, and +886 stands for Taiwan Province province of China.

All numbers are prefix numbers, which means that these numbers are used to "dial" the destination country or special administrative region. Each country also has a prefix "dial-out" country. This prefix is called the international crown code.