One thing that will cause a message to say you must dial 10 digits is wifi calling. With wifi calling you must dial every number with the full 1 (123) 555-1234 pattern to go out. I get around this problem by having all my numbers in my contact list in this format:

+1 (123) 555-1234

With the plus and the 1, the number is universal and will work locally, nationally, and internationally and with wifi calling.