I went to invite a friend of mine to the Chip app and enabled the app to access my contacts list on iOS.
Scrolling through my contacts on the Chip app I couldn’t find my friend in the list. The only thing I could think of is because there is an apostrophe used in the surname. I edited the contact and removed the apostrophe then reloaded the Chip app and I was then able to find the contact and successfully invite them to Chip. Afterwards I revoked access for Chip to see the contacts list in iOS and edited my contact back to using an apostrophe.
I believe the Chip app when accessing contacts is excluding anyone who might be using special characters in their name. I haven’t tested hyphens or other characters, it’s probably one you may need to take a look at and ensure special characters used in names are covered just something I’ve noticed which I thought you might want to be aware of.