Why are my messages rejected with reason code 53?

Messages will be rejected with reason code 53 when for the recipient of the message an invalid mobile number is set. Our API requires recipient numbers to be in international format without leading + and 00. What does this mean? This means that a number starts with the country code followed by the national number, without leading zeros.

Example: if your national number would be 08123456789 and the country code is 65, the number would be 658123456789.

The most common reasons of an invalid mobile number are:

If you believe the mobile number is correct and your message is still rejected with reason code 53, please contact our support.

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