Low balance email subject

This is the subject of the email that is sent when an account’s balance is low. Available variables are:

• <TMPL_VAR NAME=PRODUCT_NAME> the name of the Product in System -> Configuration or in custom API
• <TMPL_VAR NAME=SERVICE_EMAIL> the customer service email address from which emails to the customer appear to be coming from, as set in the rate plan
• <TMPL_VAR NAME=BALANCE> balance of the customer
• <TMPL_VAR NAME=CURRENCY_SYMBOL> currency symbol, according to the currency of the customer
• <TMPL_VAR NAME=AUTO_TOPUP> the automatic top-up amount of the customer
• <TMPL_VAR NAME=TOPUP> Boolean, takes the value of 1 if the customer’s account is to be topped-up and a top-up request has been sent
• <TMPL_VAR NAME=XXX> Name of any column xxx from table 'customers', referring to the customer that is invoiced
• <TMPL_VAR NAME=YYY> Name of any column yyy from table 'people', referring to the person that is set as contact for the customer that is invoiced