Who I have the same questioned this topic

i have an unlocked S9 and on prepaid. 

when i travel abroad i do can make phone call to US or local ,  text,  etc  but no data at all 

i am setting to "global" and roaming enabled.

the APN setting is gray out i can not change it 

so any one know why is that  and is there a fix ?

i do get the message from Verizon saying my travel pass activated and charged me $10