@T-berg - a solid red 3G indicator light usually means that your location could not be verified. We need more information.
Do you have a post paid AT&T cellular account?
Did you purchase the MicroCell used?
What do the other lights look like?
Who is your ISP and what kind of internet connection do you have (DSL, cable, or fiber)?
Sales of the MicroCell by AT&T were discontinued at the end of 2017 because the MicroCel has reached its EOL. AT&T will continue to support the MicroCell throughout next year but support will become less reliable as the year progresses. AT&T will eventually discontinue the service altogether as they get close to shutting down their 3G network. What AT&T and us recommend now is WiFi-C (WiFi Calling) if your phone is capable of that. Otherwise, your other options will be to purchase a cellular booster (see my Cellular Booster Guide, link is in my sig line), switch carriers, or possibly try Google Voice.
*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.