Why are some of our donation attempts failing?

Unfortunately, no text-to-donate service is 100% fool-proof due to the fact that users can set up limits or blocks with their mobile networks that either limits how much they can add to their mobile bill or stops them adding anything to it altogether.
We try to mitigate for these risks by allowing any supporter whose text donation fails in this way to donate by card, instead, if they wish. We call this our Donr Safety Net and it involves sending a ‘failed text donation’ text message to the supporter which includes a link to a payment page.
They can either tap this link on their smartphone or type it into their computer/tablet’s internet browser and make their donation via card instead. The page the link takes them to includes your charity’s name and the amount they tried to donate via text so they know the page is genuine and the text they receive also includes our helpline number which they’re welcome to call to check the veracity of the message, during office hours.
We keep this option as a last resort, as donations by card incur a small third-party processing fee of 1.5% + £0.20p per transaction. This fee is charged by Stripe, our third party card payment processing partner.
As long as our system receives their text, we will either process their donation or send this Safety Net message. Occasionally, however, there are some users with such stringent premium rate blocks that their text will not leave their handset (or they’re with a very small network such as Plusnet which does not currently support texts to our service). Unfortunately, in these cases, as our system has not received the text, it cannot process the donation or generate a ‘failed donation’ message.