gnpaddy to enable buying of goodybag when it goes below 300MB not below 100MB.
I am assuming by what you say that you buy your bags manually and occasionally find yourself running out of data before you get a chance to buy and start a new bag early.
In which case the answer to your problem is simple - just buy the bag earlier.
You don’t have to wait until you have 100MB remaining before you can buy another bag, that limit only applies to when you can start it.
Indeed you can buy a queued goodybag at any time during the life of a current bag.
So you could create your own “recurring goodybag” procedure by setting yourself a “buy my next bag” date on which you buy the bag. [Note: Even though the bag has been paid for it will still last a full calendar month from the day it starts.]
And as it just sits on your account ready to start - either automatically when the current one expires or manually if you need to start it early - but can also be changed / cancelled at any time up to 19.30 on the day of expiry of the old one you are in total control.
Of course it would be a good idea to set a usage alert on your phone / get a data manager app to keep you up to speed on how much data you actually have left so that you know when you need to start the new bag early as this way you should never find yourself using credit by mistake.