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Should I use this call or the Omnichannel API?
This SMS API checks whether a phone number has opted out automatically prior to sending an SMS and therefore is good for marketing SMS messages.
For transactional SMS messages we recommend using our Omnichannel messaging API as it is more featured, omnichannel capable via a single call and allows batch message submissions.

This method sends a single SMS message to a contact's mobile number.

If you want, you can send long SMS messages (greater than 160 characters), but these will incur extra costs as they count as multiple messages.

You can send an unlimited number of SMS messages through the API, and this method doesn't add to your allotted total calls per hour.

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Does not count towards your flat rate API call limit
This call is not counted as part of your flat rate hourly API call limit.

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SMS can be the target of AIT attacks, so ensure you have protection
Protect your application from automated attacks that exploit SMS and voice endpoints to generate fraudulent charges.
If you use SMS or voice API endpoints in your customer flows, you need to understand AIT (Artificially Inflated Traffic) attacks and how to defend against them. Please read our article of AIT to ensure you understand the threat and how you can protect your systems from it.