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Hello everyone,

I'm having a persistent and frustrating issue with my NotePager Pro setup. My system uses an internal modem (a Multitech USB) to send SMS messages. For the most part, it works without a hitch, but I'm getting a consistent Error 501 ('Invalid Recipient') when trying to send a message to just a few specific numbers.

I've double-checked that the numbers are correct, including the country code, and they can receive messages from other services. The modem itself seems to be functioning perfectly fine for all other recipients.

Has anyone else encountered this exact issue with a modem connection? Is there a specific modem setting or a known carrier-related problem that could cause this error for only a few valid numbers? Any ideas on how to troubleshoot this would be a huge help.
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https://ragdollhitstickman.io
Thanks!

Author	Message
Topic: Error 501 when sending to specific numbers via modem?
norwegian Replies: 1 Views: 56172	Forum: NotePager Pro Support Posted: Thu Aug 21, 2025 8:52 pm Subject: Error 501 when sending to specific numbers via modem?
norwegian Replies: 1 Views: 56172	Hello everyone, I'm having a persistent and frustrating issue with my NotePager Pro setup. My system uses an internal modem (a Multitech USB) to send SMS messages. For the most part, it works without a hitch, but I'm getting a consistent Error 501 ('Invalid Recipient') when trying to send a message to just a few specific numbers. I've double-checked that the numbers are correct, including the country code, and they can receive messages from other services. The modem itself seems to be functioning perfectly fine for all other recipients. Has anyone else encountered this exact issue with a modem connection? Is there a specific modem setting or a known carrier-related problem that could cause this error for only a few valid numbers? Any ideas on how to troubleshoot this would be a huge help. ----------- https://ragdollhitstickman.io Thanks!