SIM CARDS

RFinder takes a MICRO SIM card, and there are 2 SIM slots.
Adapters available, e.g., Verizon's nano sized SIM card fits into a B1+ with a nano to micro adapter.
☛ Here's one source of adapters on Amazon: iSYFIX Sim Card Adapter Nano Micro - Standard 4 in 1 Converter Kit with Steel Tray Eject Pin

The RFinder can be 'seen' as a Samsung Galaxy S8 for the SIM card providers (AT&T) saying it's not an approved device.

Activate the SIM card in a Verizon phone, then place into the RFinder.

No issues, most seamless.
☛ Available at MINTmobile.com and at Amazon.com

To set up the MINT APN on Android, enter the settings at:
Android 9: Android Settings | Network & Internet | Mobile Network | Advanced | Access Point Names | 3 dots | New APN
or
Android 12: Android Settings | Connections | Mobile Networks | Access Point Names | Add
or something similar depending on which Android version.

MINT Mobile APN Settings (Source: MINTmobile.com, July 22, 2023)
Once you’ve activated your plan and inserted your SIM card or installed your eSIM (for compatible phones), complete these steps.

Steps:

1. Go into your phone’s Settings
2. Select Connections or Search Access Point Names
3. Select Mobile Networks
4. Tap Access Point Names (APN)
5. Tap the 3-dot menu in the top right > Reset to default
6. Select Add to enter the following information as shown (Note: the input process is case sensitive):

APN Setting:

• Name – Mint
• APN – Wholesale
• Proxy – (leave blank)
• Port – (leave blank)
• Username – (leave blank)
• Password – (leave blank)
• Server – (leave blank)
• MMSC – (copy/paste below)

  http://wholesale.mmsmvno.com/mms/wapenc

• Multimedia Message Proxy – (leave blank)
• Multimedia Message Port – 8080
• MCC – (do not change default values)
• MNC – (do not change default values)
• Authentication Type – (leave blank) [Note: Enter PAP to get rid of those config messages when booting up.]
• APN Type – default,supl,mms,ia
• APN Protocol – IPv4/IPv6
• APN Roaming Protocol – IPv4
• MVNO type: GID
• MVNO value: 756D

Tap the three dots in the top right corner and select Save; ensure that the new Access Point Name is selected and restart your phone After your phone powers back up, you can test these new settings by sending yourself a picture message.