Bulk SMS can be an effective way to remind your donors about recurring payments and updates to their account information. Here are the steps to follow:

1. Collect phone numbers: First, you need to collect the phone numbers of your donors who have signed up for recurring payments. Make sure you have their permission to contact them via SMS.
2. Choose a bulk SMS service: There are several bulk SMS services available online. Choose one that fits your needs and budget.
3. Compose your message: Keep your message brief and to the point. Remind the donor about their upcoming payment and the amount that will be deducted from their account. If their payment is overdue, gently remind them to update their account information.
4. Personalize your message: Address your donors by their name in the message. This will make them feel more connected to your charity.
5. Include a call-to-action: Include a call-to-action in your message, such as “Please ensure that your account information is up-to-date to avoid any payment issues” or “Click the link to update your account information.”
6. Provide details: Provide details about how the donor can update their account information, such as a link to a webpage or a phone number they can call.
7. Schedule your message: Choose a date and time when most of your donors are likely to be available to receive the message.
8. Send the message: Once you have composed and scheduled your message, send it to your donors.
9. Follow up: Follow up with donors who have taken action. Thank them for updating their account information and remind them of the next payment date.
   Remember to respect your donors’ privacy and preferences. If they opt-out of receiving SMS messages, make sure you remove their phone number from your list. Also, avoid sending too many messages as it may lead to donors feeling overwhelmed and opting-out.