Communications Credits Recharge Minimum Zero
Per reference article, "What are Communications Credits," Auto Recharge should allow automatic purchase of credits when balance reaches $0. However, it's not possible to set the repurchase point for a level below $50.
Please allow a lower minimum. As credits expire annually, maintaining a minimum of $50 means wasting $50 per year.
"As such, it's recommended that you use the Auto-recharge setting to avoid any disruption of service should your Communications Credits balance reach 0 (zero). You will be sent an email when recharge transactions succeed, recharge transactions fail (such as an expired credit card), and or your Communications Credits balance reaches 0 (zero)."
"Funds will be applied only to Communications Credits at Microsoft's published rates when the services are used. Any funds not used within twelve (12) months of the purchase date will expire and be forfeited."